TWO-STAGE VEHICLE SEARCHER

Abstract

System, comprehensive: a vehicle-based communication unit (12) which includes a processor (16) wherein the processor (16) is configured to analyze request signals from a portable communication device (14); a first audible output device (40) configured to produce a first audible sound; a second audible output device (42) configured to produce a second audible sound, wherein the sound produced by the second audible output device (42) has a higher sound pressure than the sound produced by the first audible output device (40); wherein the first audible output device (40) differs from the second audible output device (42) in that the sound output of each device differs at least in pitch, quality and pattern; and wherein the processor (16) selectively activates one of the first audible output device (40) and the second audible output device (42) based on the comparison of a proximity feature of the request signals with a predetermined threshold by the processor (16).

Description

GENERAL STATE OF THE ART

[0001] The present invention relates to a system for locating a vehicle.

[0002] The functions of a car key fob typically include locking, unlocking, and trunk release, as well as emergency alarms. Car owners also use key fobs to locate their vehicles. Most key fobs and vehicles include a feature that allows, if the vehicle is parked in a crowded parking lot, the locking button on the fob to be pressed to activate an audible device attached to the vehicle, helping to locate it. Previously, when attempting to locate a vehicle in a crowded parking lot, car owners relied either on pressing an alarm button or on pressing a locking button on a key fob twice to activate either the vehicle's alarm system or a soft chirp.The vehicle owner can then wait for the audible response from the vehicle to locate it. However, the alarm and locking buttons were not designed or intended for such use. The alarm button was designed to produce an intentionally loud and harsh noise to draw attention to the vehicle and alert others. Using the alarm button as a vehicle locator reduces the effectiveness of the alarm system due to its frequent use and the perceived annoyance of triggering the alarm. It also reduces the lifespan of the horn, which is usually also used as a traffic horn. The chirp produced by pressing the locking button was designed to be gentle and pleasant for the listener to confirm that the vehicle was locked, and therefore could not be loud enough to be heard from a distance.

[0003] Patent US 8,994,548 B2, published on March 31, 2015, describes the use of an electronic device (e.g., a piezoelectric element used as a sound generator) that, unlike an emergency alarm, emits a more pleasant sound for the driver. The sound generator is capable of producing a softer, more comfortable sound when a button is pressed. When the button is pressed a second time, the duration and volume of the sound emitted by the generator increase. The problem is that if the user is not nearby (e.g., within a radius of 30-40 meters), they cannot hear the sound emitted by the generator. Consequently, the user might then resort to the alarm button, which produces a louder, but annoying, sound.The electric field generated by the high currents required to power the horn also makes it difficult to receive signals from the trailer. This forces the user to move closer to the vehicle, thus prolonging the use of the horn and the resulting, often annoying, noise. This leads to the intended sound not being used, a reduced lifespan for the horn, and customer dissatisfaction with the trailer's operation.

[0004] Other systems for locating a vehicle are shown in documents US 6 049 268 A, US 6 92 685 B2, US 7 474 208 B1, US 2009 / 0 115 639 A1, US 9 412 274 B2 and US 2015 / 0 170 516 A1, where the aforementioned documents propose using a portable communication device to cause an output device of the vehicle to produce an audible sound. BRIEF SUMMARY OF THE INVENTION

[0005] To mitigate the aforementioned problem, the present invention proposes a system according to claim 1. Preferred embodiments of the invention are the subject of the dependent claims.

[0006] The embodiments described here offer an advantage for determining the location between a portable communication device and a vehicle-based communication unit, as well as for selectively activating a sound pressure level from either a first audible output device or a second audible output device based on a proximity factor between them. The first audible output device is independent of the second audible output device, whereas the first audible output device emits a sound pressure level that is lower and has a different pitch, quality, and pattern than the sound pressure level of the second audible output device.The system uses a proximity indicator derived from data of a received vehicle function request signal and compares this indicator to a proximity threshold to determine the relative location of the portable communication device with respect to the vehicle-based communication unit. Based on whether the proximity threshold is exceeded, a determination is made as to whether sound pressure should be emitted from either the first or the second audible output device. Furthermore, if a request signal is received by the vehicle-based communication unit within a predetermined time period after a previously received request signal, the respective output device can increase the sound pressure output and / or extend the duration for which the sound pressure is emitted by that device.Proximity indicators can include, among other things, indicators of received signal strength, GPS location, flight time information, and the number of request signals.

[0007] One embodiment considers a vehicle communication device that includes a processor which analyzes request signals from a portable communication device. A first audible device generates a first sound. A second audible device generates a second sound, the second of which is louder than the first. The processor selectively activates one of the first and the second audible devices based on a comparison of a proximity feature of the request signals with a threshold value.

[0008] One embodiment considers a system comprising a vehicle-based communication unit that includes a processor. The processor is configured to analyze request signals from a portable communication device. A first audible output device is configured to generate a first audible sound. A second audible output device is configured to generate a second audible sound. The sound generated by the second audible output device is at a higher sound pressure level than that of the first audible output device. The processor selectively activates one of the first and the second audible output devices based on a comparison of a proximity feature of the request signals with a predetermined threshold set by the processor. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 illustrates a block diagram of a dual-device vehicle detector system for one vehicle. Fig. Figure 2 is a flowchart for locating a vehicle as an RSSI function. Fig. Figure 3 is a flowchart for locating a vehicle as a function of the number of received request signals. DETAILED DESCRIPTION

[0009] With reference to Fig. Figure 1 shows an exemplary dual-device detector system for a vehicle 10. The system includes a vehicle-based communication unit 12, which is attached to the vehicle 10 and communicates wirelessly with a portable communication device 14. The vehicle-based communication unit 12 can be located, for example, in a vehicle engine compartment, a vehicle dashboard, or in any other position that optimizes communication with the portable communication device 14.

[0010] The vehicle-based communication unit 12 is an electronic control unit that includes, among other things, a processor 16 and a transceiver 18. Alternatively, a transmitter and a receiver can be used instead of the transceiver 18. The transceiver 18 is coupled to an antenna 20, which is mounted on a vehicle door, a side mirror housing, an engine compartment, or other locations suitable for good performance. The vehicle-based communication unit 12 communicates with a variety of peripheral devices, including, among others, door actuators 22, trunk release devices 24, and alarm devices 26. The vehicle-based communication unit 12 also includes a received signal strength indicator (RSSI) module 27, a global positioning system (GPS) module 28, and a time-of-flight (TOF) module 29.

[0011] The portable communication device 14, also referred to as a remote keyless entry (RKE) tag, transmits RF signals to the vehicle-based communication unit 12 for remote operation of various vehicle functions, including, but not limited to, locking and unlocking the vehicle doors, unlocking the trunk, and activating the alarm. The portable communication device 14 incorporates interface buttons on one surface of the device for activating a request signal to trigger the respective vehicle function. For example, a door lock switch 30 sends wireless signals to lock the vehicle door. A door unlock switch 32 sends wireless signals to unlock the vehicle door. A trunk unlock switch 34 sends wireless signals to unlock the trunk or tailgate.An alarm switch 36 sends wireless signals to activate and deactivate a vehicle alarm. The portable communication device 14 typically transmits the RF signals at a maximum power level regulated by the Federal Communications Commission (FCC). It is understood that the RF signal transmission may include Bluetooth and UWB. The RF signals are received by the portable communication device 14 when the vehicle-based communication unit 12 is within the transmission range of the portable communication device 14, and the RF signals are authenticated before a vehicle function is activated.While the portable communication device 14 is described here as an RKE trailer, the portable communication device 14 may include, among other things, a telephone, smartphone or any other portable device that can transmit signals directly or indirectly to the vehicle using an intermediate system, such as a cloud.

[0012] The portable communication device 14 further includes a processor 38, which is coupled to the interface buttons, which contain separate switches 39 for activating the various RKE commands. The portable communication device 14 further includes a transceiver 37, which is coupled to an antenna 41. The antenna 41 functions, on the one hand, as a receiving antenna for capturing RF energy and delivering the signal to the transceiver 37 for signal processing, and on the other hand, as a transmitting antenna for receiving signals from the transceiver 37 and generating an RF field for signal transmission.

[0013] Each RKE command is initiated by pressing down a respective interface button on the portable communication device 14, which causes a signal to be transmitted wirelessly via the RF transceiver 37 and the antenna 41 to the vehicle-based communication unit 12, requesting the execution of the vehicle function that is assigned to the respective interface button.

[0014] A specific function, associated with the door locking function, is activated when the locking button is pressed twice within a short time period (e.g., 3 seconds), producing an audible sound that verifies the vehicle is locked. Users have also frequently employed this function as a vehicle locator when the vehicle was parked in a crowded parking lot (e.g., shopping mall, sporting event, etc.). The system, as described here, utilizes a first audible output device 40 and a second audible output device 42, which are distinct and independent of each other. The second audible output device 42 generates a sound pressure level (decibel level) that is higher than that of the first audible output device 40.The first audible output device 40 differs from the second audible output device 42 in that the sound output by each device can differ in at least one aspect of pitch, quality, and pattern. For example, the first audible output device 40 may include, among other things, a piezoelectric device, whereas the second audible output device 42 may include, among other things, a horn. However, the second audible output device 42 generates a higher sound pressure level than the first audible output device 40. Consequently, either the first audible output device 40 or the second audible output device 42 can be selected to generate the sound based on a threshold being exceeded, or the system can dynamically switch between the first audible output device 40 and the second audible output device 42 based on the threshold being exceeded.The exceeded threshold may include, among other things, a predetermined number of times a respective button on the portable communication device 14 is pressed, an RSSI threshold, a GPS difference threshold, or a flight time threshold that determines the distance of the device 14 to the vehicle 10.

[0015] In an example configuration, a specific button (e.g., the locking button) is pressed twice in succession within a specific time interval (e.g., 3 seconds). Subsequent presses of the button activate the first audible output device 40 of the vehicle 10. An audible sound is generated by the first audible output device 40, exhibiting a predefined sound pressure level for a predetermined duration. If the button is subsequently pressed again within a predetermined time interval following a previous button press, the sound pressure level generated by the first audible output device 40 is increased. Additionally, the duration for which the sound pressure level is emitted by the first audible output device 40 can be extended.Furthermore, if the respective button is subsequently pressed within the predetermined time period following a previous button press, the sound pressure of the first audible device 40 can increase by a predetermined amount, and the duration for which the sound pressure is emitted by the first audible output device 40 can also be extended. Subsequent activations of the respective button with a predetermined duration can increase both the sound pressure emitted by the first audible output device 40 and the duration for which the sound pressure is emitted, until a predetermined threshold is exceeded. When the number of times the respective button is pressed reaches the predetermined threshold, the second audible output device 42 is activated for each subsequent button press to generate the sound pressure.This means that each time the respective button is pressed within the predetermined time period following a previous button press, the second audible output device 42 generates a corresponding sound pressure level. It is understood that the sound pressure level generated by the second audible output device 42 and / or the duration for which the sound pressure level is generated by the second audible output device 42 can be increased, similarly to the first audible output device 40, if a subsequent button is pressed within the predetermined time period following the previous button press.

[0016] In yet another configuration, the threshold can be based on the received signal strength from the RSSI module 27. The received signal strength is obtained by a receiver circuit of the vehicle-based communication unit 12, which identifies the signal strength of each received message. When the signal is received by the transceiver 18 of the vehicle-based communication unit 12, the RSSI module 27 measures the signal strength of the received signal. The RSSI is an indication of the power of the received signal, providing an indication of the proximity of the portable communication device 14 to the vehicle-based communication unit 12. The higher the RSSI value, the closer the communication devices are to each other.To utilize the RSSI, the signal strength, as determined by the RSSI module 27, is used to correlate a relative distance between the vehicle-based communication unit 12 and the portable communication device 14. Depending on whether the RSSI value exceeds the predetermined threshold, the vehicle-based communication unit 12 would determine whether to use the first audible output device 40 or the second audible output device 42. For example, if the RSSI value is above an RSSI threshold, it is determined that the communication devices are within a certain distance of each other, and the first audible output device 40 is used.Alternatively, if the RSSI value is below an RSSI threshold, it is determined that the communication devices are not within a certain distance of each other, whereby the second audible output device 42 would be used. It is understood that the sound from a second device 42 is demonstrably, mathematically or empirically, clearly audible at the larger of the distances corresponding to the RSSI thresholds, and that the first audible output device 40 is demonstrably, mathematically or empirically, inaudible at the lower RSSI threshold.

[0017] In each situation, when the driver either approaches or moves away from the vehicle, a corresponding button is pressed, and the signal is transmitted from the portable communication device 14 to the vehicle-based communication unit 12. Upon receiving the signal, the RSSI module 27 within the vehicle-based communication unit 12 determines the signal strength. If the RSSI value exceeds a certain RSSI threshold, it is determined that the portable communication device 14 is within a certain distance of the vehicle at which the first audible output device 40 is used. The first audible output device preferably emits a less obtrusive and more pleasant sound compared to the sound output by the second audible output device 42.The RSSI value exceeding the predetermined threshold is correlated with a distance at which the user is within a specified range of the vehicle and can hear the sound produced by the first audible output device 40. While the user continues to press the respective button, an RSSI check is performed for each received signal, and it is determined whether the RSSI value for each signal is above or below the RSSI threshold. If the RSSI value is below the RSSI threshold, the second audible output device 42 is used to produce a sound that is louder than and distinct from the sound produced by the first audible output device 40.It is understood that if any subsequent signals indicate that the RSSI value received by the vehicle-based communication unit is above the RSSI threshold, the system switches between outputting a sound from the second audible output device 42 and outputting a sound from the first audible output device 40. For example, if a user initially presses a respective button and the vehicle-based communication unit determines that the RSSI value is below the RSSI threshold, a sound is output through the second audible output device 42. If the user presses the respective button and the RSSI value is above the RSSI threshold, this indicates that the user has moved closer to the vehicle and that the sound from the first audible output device 40 can be heard by the user.The vehicle emits sound from the first audible output device 40, which is a less noticeable and more pleasant sound compared to the sound from the second audible output device. Alternatively, the sound output can switch from the first audible output device 40 to the second audible output device 42 when the user moves from an area where the RSSI value exceeds the RSSI threshold to areas where the RSSI value is below the RSSI threshold.

[0018] Furthermore, if a user, while in a range where the RSSI value is either below or above the RSSI threshold, subsequently presses the button within a predetermined time interval from a previous button press, each subsequent press can increase the volume of the respective output device as well as the duration for which the sound is emitted. For example, if it is determined that the user is in a range where each successive press of the button causes the RSSI to exceed the predetermined threshold, then for each subsequent button press within a predetermined time interval from a previous button press where each RSSI value for each transmitted signal remains above the RSSI threshold, the sound pressure level emitted by the first audible output device will be greater than the previous sound pressure level emitted by the first audible output device.Furthermore, the duration for which the sound is emitted can increase with each subsequent button press. The same process can be used while a user presses the respective button within the range that causes the RSSI value to fall below the RSSI threshold.

[0019] Another configuration allows the RSSI threshold to be set based on either measured noise levels or areas where high noise levels are expected. For example, the vehicle hands-free microphone 50 can be activated when the user presses the corresponding button. The hands-free microphone receives and analyzes the ambient noise it picks up. Based on the analysis results, the processor 16 within the vehicle-based communication unit sets the RSSI threshold. That is, if the ambient noise exceeds a predetermined ambient noise threshold, the processor 16 adjusts the RSSI threshold so that the second audible output device 42 is activated more quickly when elevated ambient noise levels exceed a certain threshold.

[0020] Another configuration option is to set the RSSI threshold if the vehicle is parked in an area where elevated ambient noise levels are expected. Examples of parking areas with ambient noise levels exceeding the predetermined threshold include airports, shopping malls, areas adjacent to highways or major roads, stadiums, and amusement parks. Similarly, GPS coordinates or other data can be compared with a map database to determine if the parking area is located in a region with elevated ambient noise levels.

[0021] Another configuration could use temperature data to adjust the output of the first audible output device 40 and the second audible output device 42. Sound travels further, for example, in colder conditions. Therefore, the system settings at the audible output devices could be based on a temperature measurement, the season (e.g., winter versus summer), or the time of day (day versus night).

[0022] Another configuration could utilize GPS data. If the portable communication device 14 is a device that includes a GPS function (e.g., a smartphone), the vehicle could compare the phone's GPS position and the vehicle's GPS position to determine a relative distance between them to trigger either the first audible output device 40 or the second audible output device 42. If the vehicle includes a GPS module 52, the vehicle's GPS coordinates are stored in a vehicle memory when the user exits the vehicle. Alternatively, if the vehicle does not have a GPS module, the vehicle-based communication unit 12 communicates with the portable communication device 14 (e.g., a smartphone).The GPS coordinates of the portable communication device 14 (e.g., a smartphone) are communicated to and stored in a vehicle memory, thus providing the vehicle with its own GPS coordinates. Each time the corresponding button on the portable communication device 14 is subsequently pressed, a signal containing the current GPS coordinates of the portable communication device is sent to the vehicle-based communication unit 12. The processor 16 compares the transmitted GPS coordinates with the stored GPS coordinates. Based on whether the relative distance between the portable communication device and the vehicle-based communication unit 12, as determined by comparing the GPS coordinates, exceeds the predetermined distance threshold, it is determined whether the first audible output device 40 or the second audible output device 42 is used.In cases where the portable communication device 14 is a smartphone, it can communicate directly with the vehicle via Bluetooth, Wi-Fi, or other wireless solutions, and / or it can also be capable of sending vehicle search commands via cellular network (e.g., the phone communicates with a cloud, and the cloud communicates with the vehicle). In cases where a cellular vehicle search command has been issued, it may be sufficient to switch directly to the second output device 42. It is understood that the sound from a second device 42 is demonstrably, mathematically or empirically, clearly audible at the larger of the distances corresponding to the distance thresholds, as determined by the GPS position, and that the first audible output device 40 is demonstrably, mathematically or empirically, inaudible at the smaller distance threshold determined by the GPS position.

[0023] Another configuration uses time-of-flight (TOF) to determine whether to use the first audible output device 40 or the second audible output device 42. Time-of-flight is a technique that measures the time it takes for an object, particle, or acoustic, electromagnetic, or other wave to travel a certain distance through a medium. Because TOF provides a highly accurate estimate, this measurement can be used to estimate the user's ability to hear the activated audible output device.For example, using ultra-wideband radio technology or another radio technology of a portable communication device, a relative distance between the portable communication device 14 and the vehicle 10 can be determined; or the relative distance between the first audible output device 40 and the second audible output device 42 can be determined by determining the time-of-flight (TOF). It is then determined whether the TOF measurement exceeds a predetermined TOF threshold to determine which audible output device should be used.

[0024] It is understood that the sound from a second output device 42 is mathematically or empirically demonstrably clearly audible at the larger distance corresponding to the distance thresholds as determined by the TOF measurement, and that the first audible output device 40 is mathematically or empirically demonstrably not audible at the smaller distance threshold determined by the TOF measurement.

[0025] Fig. Figure 2 illustrates a flowchart for a procedure for activating a respective audible output device to locate a vehicle based on the received signal strength of the signal transmitted by the portable communication device.

[0026] In step 60, the vehicle-based communication unit is activated to monitor for incoming signals from the portable communication device.

[0027] Step 61 determines whether a request signal is received from the portable communication device. If a request signal is received, the routine proceeds to step 62; otherwise, the routine returns to step 60.

[0028] In step 62, the RSSI value of the signal is obtained, and it is determined whether the RSSI value is above the RSSI threshold. If the RSSI value is above the predetermined threshold, the routine proceeds to step 63; otherwise, the routine proceeds to step 67.

[0029] In step 63, in response to the RSSI exceeding the RSSI threshold, a sound is generated by the first audible output device. The first audible output device produces a sound pressure level that is lower relative to the second audible output device.

[0030] Step 64 determines whether a subsequent request signal generated by the portable communication device is received by the vehicle-based communication unit within a predetermined time from the previous request signal. If a subsequent signal is received within the predetermined time, the routine proceeds to step 65; otherwise, the routine returns to step 60 to monitor for request signals.

[0031] Step 65 determines whether the RSSI value is above the RSSI threshold. If it is determined that the RSSI value is above the RSSI threshold, the routine proceeds to step 66. If it is determined that the RSSI value is below the RSSI threshold, the routine proceeds to step 67, which uses the second audible output device.

[0032] In step 66, the first output device generates a sound with a higher sound pressure level than the previous sound output. The sound emitted by the first audible output device may be greater than the previous sound emitted by the first audible output device in terms of sound pressure and / or duration. The routine then returns to step 64 to determine whether a subsequent request signal is received by the portable communication device.

[0033] In response to a determination in step 62 or step 65 that the sound pressure is below the RSSI threshold, and with reference to step 67, in response to the RSSI being below the RSSI threshold, a sound is generated by the second audible output device. The second audible output device generates a sound pressure that is greater relative to the first audible output device.

[0034] Step 68 determines whether a subsequent request signal generated by the portable communication device is received by the vehicle-based communication unit within a predetermined time from the previous request signal. If a subsequent signal is received within the predetermined time, the routine proceeds to step 69; otherwise, the routine returns to step 60 to monitor for request signals.

[0035] Step 69 determines whether the RSSI value of the following signal is below the RSSI threshold. If it is determined that the RSSI value is below the RSSI threshold, the routine proceeds to step 70. If it is determined that the RSSI value is above the RSSI threshold, the routine proceeds to step 63, which uses the first audible output device.

[0036] In step 70, in response to the determination that the RSSI is below the RSSI threshold, the second output device generates a sound with a higher sound pressure level than the previous sound output. The sound emitted by the second audible output device may also be longer in duration than the previous sound emitted by the second audible output device. The routine then returns to step 68 to determine whether a subsequent request signal is received by the portable communication device.

[0037] Fig. Figure 3 illustrates a flowchart for a procedure to activate a respective audible output device to locate a vehicle based on a number of subsequent inputs to the portable communication device by a user.

[0038] In step 80, the vehicle-based communication unit monitors for two consecutive signals from the portable communication device within the predetermined time period.

[0039] Step 81 determines whether two consecutive signals are received within the predetermined time period. If the two request signals are present, the routine proceeds to step 82; otherwise, the routine returns to step 80.

[0040] In step 82, an audible sound pressure is emitted through the first audible output device.

[0041] Step 83 determines whether a subsequent request signal is received by the portable communication device within a predetermined time period from the previous request signal. If the request signal is received within the predetermined time period, the routine proceeds to step 84; otherwise, the routine returns to step 80.

[0042] Step 84 determines whether the total number of consecutive received request signals, each received within the predetermined time period from each previous request signal, exceeds a predetermined request threshold. If the number of consecutive received request signals exceeds the predetermined request threshold, the routine proceeds to step 85; otherwise, the routine returns to step 80.

[0043] In step 85, in response to the number of consecutive received request signals exceeding the predetermined request threshold, sound is emitted through the second audible output device. The second audible output device has a sound pressure level greater than the first audible output device. The routine then returns to step 83.

[0044] While certain embodiments of the present invention have been described in detail, those skilled in the field concerned with this invention will recognize several alternative designs and embodiments for carrying out the invention as defined by the following claims.

Claims

[1] System, encompassing: a vehicle-based communication unit (12) which includes a processor (16) wherein the processor (16) is configured to analyze request signals from a portable communication device (14); a first audible output device (40) configured to produce a first audible sound; a second audible output device (42) configured to produce a second audible sound, wherein the sound produced by the second audible output device (42) has a higher sound pressure than the sound produced by the first audible output device (40); wherein the first audible output device (40) differs from the second audible output device (42) in that the sound output of each device differs at least in pitch, quality and pattern; and wherein the processor (16) selectively activates one of the first audible output device (40) and the second audible output device (42) based on the comparison of a proximity feature of the request signals with a predetermined threshold by the processor (16). [2] System according to claim 1, wherein the proximity feature of the request signal includes an indicator of the received signal strength (RSSI) and the predetermined threshold is an RSSI threshold, wherein the RSSI is determined each time a request signal is received from the portable communication device (14) at the vehicle-based communication unit (12). [3] System according to claim 2, wherein the processor (16) activates the first audible output device (40) when the RSSI is above the RSSI threshold, and wherein the processor (16) activates the second audible output device (42) when the RSSI is below the RSSI threshold. [4] System according to claim 3, wherein the sound pressure of the first audible output device (40) is gradually increased in response to the fact that a subsequent request signal is received by the vehicle-based communication unit (12) within a predetermined time period from a previous request signal received by the vehicle-based communication unit (12). [5] System according to claim 3, wherein the duration of the sound pressure output by the first audible output device (40) is gradually increased in response to a subsequent request signal being received by the vehicle-based communication unit (12) within a predetermined time period from a previous request signal received by the vehicle-based communication unit (12). [6] System according to claim 3, wherein the sound pressure of the second audible output device (42) is gradually increased in response to the fact that a subsequent request signal is received by the vehicle-based communication unit (12) within a predetermined time period from a previous request signal received by the vehicle-based communication unit (12). [7] System according to claim 3, wherein the duration of the sound pressure output by the second audible output device (42) is gradually increased in response to a subsequent request signal being received by the vehicle-based communication unit (12) within a predetermined time period from a previous request signal received by the vehicle-based communication unit (12). [8] System according to claim 2, wherein the proximity feature of the request signals includes a GPS position and the predetermined threshold is a distance threshold, wherein a distance between the portable communication device (14) and the vehicle-based communication unit (12) is based on a function of a GPS position of the portable communication device (14) and a GPS position of the vehicle-based communication unit (12), and wherein a GPS position of the portable device is communicated in each request signal received by the vehicle-based communication unit (12). [9] System according to claim 8, wherein the vehicle-based communication unit (12) receives the GPS position of the vehicle from a GPS module inside the vehicle (10). [10] System according to claim 8, wherein the vehicle-based communication unit (12) receives the GPS position of the portable communication device (14) before the portable communication device (14) leaves the vehicle (10). [11] System according to claim 8, wherein the processor (16) activates the first audible output device (40) when the distance between the GPS position of the vehicle (10) and the GPS position of the portable communication device (14) is below the distance threshold. [12] System according to claim 8, wherein the processor (16) activates the second audible output device (42) when the distance between the GPS position of the vehicle (10) and the GPS position of the portable communication device (14) is below the distance threshold. [13] System according to claim 1, wherein the proximity feature of the request signals includes a request signal number and the predetermined threshold is a predetermined count value, wherein the request signal number is incremented each time a respective request signal is received within a predetermined time period from a previous request signal. [14] System according to claim 13, wherein the processor (16) activates the first audible output device (40) when the request signal number is below the predetermined number, and wherein the processor (16) activates the second audible output device (42) when the request signal number is above the predetermined number.

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