Power supply management for a wireless tracking device with a limited power source

Abstract

A wireless tracking device (122), comprising: a location device configured to determine a geographic position of the wireless tracking device (122); at least one sensor (250, 254, 258, 262) configured to generate a sensor signal representing a state or property associated with the wireless tracking device (122); at least one control unit (210, 214) coupled to the location device and the at least one sensor (250, 254, 258, 262), wherein the at least one control unit (270, 272) is configured to: to generate a message indicating the geographic position, state or property associated with the wireless tracking device (122); to put the wireless tracking device (122) into a first mode; and to switch the wireless tracking device (122) into a second mode that consumes more power than the first mode in response to a sensor signal representing a predefined event; and a communication module (226) configured to send the message over a wireless network, where at least one control unit (210, 214) remains configured to: to calculate (514) an estimated time of arrival of the wireless tracking device at a geographical region (410) where the message is not to be sent over the wireless network; to determine an interval to switch the wireless tracking device (122) from the first mode to the second mode (518); and to determine whether to switch to the second mode, based on the specified interval.

Description

1. Field of the invention

[0001] The invention relates to controlling the operation of a wireless tracking device with a limited power source, more specifically to operating the wireless tracking device in more than one operating mode to reduce power consumption and extend its operating time. 2. Background of the invention

[0002] Wireless tracking devices are used to track the positions and conditions of various assets. Such wireless tracking devices are often mounted on the assets or placed near them. As the assets are transported or exposed to a changing environment, the wireless tracking devices capture the position and / or detect changing conditions of the assets. The wireless tracking devices then send wireless messages indicating the positions and / or other environmental parameters of the assets to a remote monitoring station. Based on the collected information, the remote monitoring station can initiate actions such as sending reports to customers, taking remedial measures to prevent deterioration of the assets, and arranging the recovery of stolen assets.Furthermore, a system and a method for the spontaneous tracking of assets are known from US 2008 / 0086391 A1.

[0003] Generally, a wireless tracking device contains various components and sensors enclosed in a housing. The housing provides robust protection against dirt and other contaminants, as well as external forces. The wireless tracking device can contain various components, such as temperature sensors, humidity sensors, light sensors, accelerometers, gyroscopes, magnetometers, controllers, GPS modules, and wireless communication modules. These components or modules may consume power during operation. Some wireless tracking devices include sensors to accommodate different applications, whereas others are equipped with fewer types of sensors chosen for specific applications.

[0004] To power these components and modules, a wireless tracking device incorporates a limited power source such as batteries or solar cells. In many cases, wireless tracking devices operate in environments where access to other power sources is unavailable. Wireless tracking devices often rely on a limited power source for their operation. Therefore, to increase the uptime of a wireless tracking device, it is necessary to reduce the power consumption of its components. Summary of the invention

[0005] The invention relates to a wireless tracking device, as well as a method and a computer-readable storage medium according to the independent patent claims. Embodiments relate to a wireless tracking device that operates in at least two operating modes to reduce power consumption. In a sleep mode (hibernation mode), the wireless tracking device switches off the components that consume a lot of power to save power. The wireless tracking device is temporarily switched to an active mode, in which the components that consume a lot of power are switched on. As soon as an event is detected, the wireless tracking device switches from sleep mode to active mode to track positions or to detect changes in its environment. The wireless tracking device can return to sleep mode if no further events are detected or a preset period of time has elapsed.

[0006] In one embodiment, the components that are powered off in sleep mode include a location determining device for determining the location of the wireless tracking device and a communications module for sending the message over a wireless network. The location determining device and the communications module consume a lot of power, and therefore, these components are temporarily operated in active mode to conserve power.

[0007] In one embodiment, the wireless tracking device includes two control units. One control unit consumes less power than the other. The control unit that consumes less power remains powered on in both active mode and sleep mode. In contrast, the control unit that consumes more power is selectively powered on during active mode to control high-power components.

[0008] In one embodiment, a geofence is established for an area that has low connectivity to the wireless network. The wireless tracking device determines proximity to the geofence and switches to active mode at a higher frequency to detect whether the wireless tracking device has entered the geofence and to send updated messages before the wireless tracking device has entered the geofence.

[0009] The features and advantages described in the specification are not exhaustive, and many additional features and advantages will be apparent to a person skilled in the art in light of the drawings, the specification, and the claims. Furthermore, it should be noted that the language used in the specification has been chosen primarily for readability and educational purposes. Brief description of the drawings Fig. 1 shows a conceptual diagram of a wireless tracking device in a vehicle, according to one embodiment. Fig. 2 shows a block diagram of a wireless tracking device, according to one embodiment. Fig. 3 shows a flow diagram of a method of operating the wireless tracking device in more than one mode, according to one embodiment. Fig. 4 shows the representation of a geofence with various associated operating modes, according to one embodiment. Fig. Figure 5 shows a flowchart of the process of switching between the active mode and the sleep mode when the geofence is implemented. Detailed description of the invention

[0010] Embodiments described herein provide a wireless tracking device that operates in at least two modes to reduce power consumption and extend the operating time of the wireless tracking device. In an active mode, the wireless tracking device activates a communication module to communicate with a remote device via a wireless connection or other high-power components. In sleep mode, the components or modules in the wireless tracking device are shut down to reduce power consumption. The wireless tracking device can selectively switch from sleep mode to active mode when a predefined event is detected. Example use of the wireless tracking device

[0011] Fig. 1 shows an illustration of a wireless tracking device 122 in a moving vehicle 120. The wireless tracking device 122 may be placed in a cargo item 126 being transported by the vehicle 120. In this example, the wireless tracking device 122 tracks its position using a Global Positioning System (GPS) module that detects signals from satellites 110. The wireless tracking device 122 in cargo items 126 also communicates with a remote monitoring station 128 via a wireless communication channel 130.

[0012] The vehicle 120 may transport multiple units of cargo 126, each unit equipped with a wireless tracking device. Each cargo 126 may be destined for a different destination. As the cargo 126 is transported, a wireless tracking device 122 attached to the cargo 126 tracks the position of the cargo 126 and the environmental conditions surrounding the cargo 126. The position and other environmental information are then transmitted to a monitoring station 128 in a wireless message.

[0013] The environmental conditions detected by the wireless tracking device 122 may include, but are not limited to, temperature, humidity, light, noise, vibration, tilt angle, shock, certain types of chemical compounds, pressure, magnetic fields, smoke, and motion. The wireless tracking device can be configured to detect some or all of these environmental conditions.

[0014] The use of the wireless tracking device 122 is not limited to moving cargo 126. The wireless tracking device 122 may be used for an object that remains stationary. In such a case, the wireless tracking device 122 is primarily used to detect environmental conditions surrounding the wireless tracking device 122. Furthermore, the vehicle 120 is only one example of a type of transportation. The wireless tracking device 122 and the cargo 126 may be transported by other types of transportation, such as by ship, rail, or aircraft. The cargo 126 may be any item transported commercially, including, but not limited to, envelopes, packages, express mailers, boxes, pallets, containers, crates, and specialty products and materials. Example structure of a wireless tracking device

[0015] The wireless tracking device 122 operates in two different modes: an active mode and a sleep mode. In active mode, most or all components in the wireless tracking device are enabled. The enabled components include high-power components, such as a wireless communications module. In sleep mode, a smaller number of components or modules in the wireless tracking device are enabled. Other components or modules are disabled to conserve power. The wireless tracking device 122 switches between the active mode and the sleep mode in response to the detection of, or in anticipation of, an event.

[0016] Fig. Figure 2 shows a block diagram of a wireless tracking device according to one embodiment. The wireless tracking device 122 may include, among other components, a high-power system controller 210, a low-power system controller 214, a Global Positioning System (GPS) module 222, a wireless communication module 226, a power manager 230, a limited power source 234, and various sensors 250-262. The wireless tracking device 122 may include other components not shown in Fig. 2, such as an input module or speaker.

[0017] The wireless tracking device 122 from Fig. 2 has a dual-processor structure that includes two controllers: the high-power system controller 210 and the low-power system controller 214. Using the two controllers allows for reduced power consumption in sleep mode, while achieving high computing performance during active mode. When the wireless tracking device 122 is placed in active mode, the high-power system controller 210 becomes active and performs power-intensive operations. Such power-intensive operations include, for example, determining the location of the wireless tracking device 122 using the GPS module 222 and wirelessly communicating with the remote monitoring station 128 via the wireless communication module 226.During sleep mode, the wireless tracking device 122, the GPS module 222, and the wireless communication module 226 may be disabled to reduce power consumption.

[0018] In one embodiment, the low-power system controller 214 is embodied as an ATMEGA 8-bit microcontroller (available from Atmel Corporation, San Jose, California), an Energy Micro Gecko microcontroller (available from Energy Micro AS, Oslo, Norway), or a SAM3 microcontroller (available from Atmel Corporation, San Jose, California). Examples of the high-power system controller 210 include the Marvell PXA series, ARM11, CPositionenx-A series, or TI DSPs.

[0019] In one embodiment, the high power system controller 210 controls the operation of the GPS module 222 and the communications module 226. When the high power system controller 210 is turned off, the GPS module 222 and the wireless communications module 226 are also disabled to reduce power consumption.

[0020] The low-power system controller 214 remains active in both the active mode and the sleep mode. The low-power system controller 214 determines whether the wireless tracking device 122 is switched to the active mode or the sleep mode, as described in detail below with reference to Fig. 3. In one embodiment, the low-power system controller 214 is connected to low-power components, such as sensors 250-262. The low-power system controller 214 continuously receives sensor signals 282-294 even in sleep mode to avoid the loss of meaningful sensor data. However, the sampling rate and sensitivity of the sensor signals 282-294 may be reduced in sleep mode to reduce power consumption.

[0021] The low-power system controller 214 sends commands to the power manager 230 to turn power on or off to the high-power system controller 210. When the low-power system controller 214 issues a command indicating that the wireless tracking device 122 should be placed in sleep mode, the power manager 230 turns off power to the high-power system controller 210.

[0022] Power supply manager 230 is connected to power source 234. Power source 234 may be a limited power source, such as a battery or solar cells. In one embodiment, power source 234 includes a charging unit. The charging circuit receives electrical charging current through port 238 to charge the battery.

[0023] The GPS module 222 may include an antenna and a signal processing unit for receiving GPS signals. The GPS module 222 operates under the command of the high-power system controller 210 to identify the current position of the wireless tracking device 122. In one embodiment, the GPS module 222 is implemented as A-GPS (Assisted GPS), which improves startup performance or TTFF (Time To First Fix) by utilizing data received via the wireless communication module 226. To this end, the GPS module 222 receives ephemeris data from a remote server via the wireless communication module 226.

[0024] The wireless communication module 226 includes a transceiver for sending or receiving data from a remote monitoring station 128. The wireless communication module 226 can establish communication using various communication protocols such as GSM, Wi-Fi, Bluetooth, Zigbee, UMTS / HSxPA, 3GPP Long Term Evolution (LTE), and WiMAX.

[0025] Sensors 250 to 262 detect various physical properties or conditions and transmit sensor signals 282 to 294 to the low-power system controller 214. The sensors in the wireless tracking device 122 include, for example, an accelerometer 250, a light sensor 254, a temperature sensor 258, and a humidity sensor 262. The wireless tracking device 122 may include other types of sensors to detect various physical properties or conditions.

[0026] The high-power system controller 210 and the low-power system controller 214 communicate via a data bridge 212. The high-power system controller 210 can receive the sensor data from the low-power system controller 214, compile the sensor data into a message, and send the message to the remote monitoring station 128 via the wireless communication module 226. On the other hand, the low-power system controller 214 receives location information (based on the GPS module 222) from the high-power system controller 210 or any data (e.g., control commands) from the remote monitoring station 128 via the data bridge 212.

[0027] The high-power system controller 210 and the low-power system controller 214 include a computer-readable storage medium 270 and a computer-readable storage medium 272, respectively. The computer-readable storage medium 270 stores instructions for execution by the high-power system controller 210. The computer-readable storage medium 272 stores instructions for execution by the low-power system controller 214. In one embodiment, the computer-readable storage media 270, 272 are embodied as non-volatile storage devices (e.g., EEPROM (Electrically Erasable Programmable Read-Only Memory) or Flash memory), as volatile storage devices (e.g., Random Access Memory (RAM), random access memory), or as a combination of both.

[0028] The embodiment of Fig. 2 is for illustrative purposes only. Wireless tracking devices with other configurations may also be used. For example, a single processor architecture may be used, which includes only a single controller. In the single processor architecture, all components and sensors are connected to and controlled by the single controller. In one embodiment, the single controller may operate in two modes: an active mode with increased processor performance and a sleep mode with reduced processor performance. In another embodiment, the controller 210 for the high-power system and the controller 214 for the low-power system could also be implemented in a multi-core configuration or via virtualization with a single processor core. Scheme for switching the power mode

[0029] Fig. Figure 3 shows a flowchart of a method for placing the wireless tracking device 122 into active mode or sleep mode, according to one embodiment. The low-power system controller 214 receives 310 the sensor signals 282 to 294 from the sensors 250 to 262 or the position of the wireless tracking device from the GPS module 222. For this purpose, the low-power system controller 214 stores commands to switch the power modes in the computer-readable storage medium 272.

[0030] Then, the low-power system controller 214 determines 312 whether one or more predefined events are detected to switch the wireless tracking device 122 to active mode. Various types of events can be used to switch modes. The wireless tracking device 122 is switched to active mode when events of interest to a user are likely to occur or continue, whereas the wireless tracking device 122 is placed in sleep mode when the events of interest are unlikely to occur or continue.

[0031] When one or more predefined events are detected, the low-power system controller 214 switches the wireless tracking device 122 to or maintains it in active mode 314. In one embodiment, the predefined events include detecting movement of the wireless tracking device 122 by the accelerometer or the speed of the wireless tracking device 122 above a threshold. While the wireless tracking device 122 is in active mode, the low-power system controller 214 may monitor location changes based on GPS signals from the current active mode session to determine the speed of the wireless tracking device 122.Alternatively, the low power system controller 214 may compare the position of the wireless tracking device 122 with the position of the wireless tracking device 122 in the previous active mode session to determine the speed of the wireless tracking device 122.

[0032] In one embodiment, the wireless tracking device 122 is switched to or maintained in active mode 314 when external events are detected via sensors 250-262. The external events refer to events that occur outside the wireless tracking device 122 and may include, for example, (i) movement of the wireless tracking device 122 (as detected by the accelerometer 250), (ii) changes from outdoors to indoors or vice versa (as detected by the light sensor 254), (iii) temperature changes (as detected by the temperature sensor 258), (iv) changes in humidity (as detected by the humidity sensor 262), and (v) detection of certain chemical compounds or smoke. When such external events are detected, events of interest are likely to follow or continue.Therefore, the wireless tracking device 122 is maintained in active mode to collect data associated with the external events.

[0033] In one embodiment, the event may be the passage of time or a signal from a timer indicating a predefined time. The low-power system controller 214 may periodically switch the wireless tracking device 122 to active mode. The low-power system controller 214 switches the active mode more often or remains in active mode for a longer period of time when the accelerometer 250 sends a signal 282 indicating movement of the wireless tracking device 122. The wireless tracking device 122 is more likely to experience significant changes in the environment when the wireless tracking device 122 is transported. Therefore, the wireless tracking device 122 is switched to active mode to send more frequent updates to the remote monitoring station.The low power system controller 214 may return to sleep mode after a specified period of time has elapsed.

[0034] If no significant events are detected for a predefined period of time, the low-power system controller 214 switches 318 or leaves the wireless tracking device 122 in sleep mode. The wireless tracking device 122 is unlikely to experience significant changes if predefined events are not detected. Therefore, the low-power system controller 214 switches the wireless tracking device 122 into sleep mode to conserve power.

[0035] After the wireless tracking device 122 is switched to or maintained in active mode or sleep mode 314, 318, the process returns to receiving 310 the sensor signals or positions.

[0036] In one embodiment, more significant events in the sensor signals or more drastic changes in position are required to switch the wireless tracking device 122 from sleep mode to active mode compared to the events required to leave the wireless tracking device 122 in active mode. The sensitivity of the sensors (e.g., accelerometer 250) is reduced in sleep mode to prevent the wireless tracking device 122 from being awakened to active mode due to minor changes in the sensor signals.

[0037] In contrast, the sensitivity of the sensors is increased when the wireless tracking device 122 is currently in active mode. The fact that the wireless tracking device 122 is currently in active mode indicates that the wireless tracking device 122 is likely experiencing other significant events. By adjusting the sensitivity to sensor signals and location changes based on the mode of the wireless tracking device 122, the wireless tracking device 122 can be prevented from being awakened due to non-significant events while maintaining the chance of detecting significant events. Geofencing of the wireless tracking device

[0038] The wireless tracking device 122 may move through a geographic region where wireless communication is unavailable or where wireless communication reception is poor. In one embodiment, such a geographic region may be established as a geofence, within which the wireless tracking device 122 will not attempt to communicate with the remote monitoring station 128. A geofence refers to a geographic region artificially defined for one purpose or another. By avoiding communication within the geographically limited area, the power consumption associated with attempts to communicate with the remote monitoring station 128 can be avoided in an area with poor reception. Additionally, this feature may be used to meet certain regulatory requirements in specific areas.

[0039] Fig. Figure 4 shows a representation of a geofence 410 linked to the wireless communication of the wireless tracking device 122 where wireless communication is unavailable or signal reception is poor. Within the geofence 410, the wireless tracking device 122 does not attempt to communicate with the remote monitoring station 128. Data collected for events while the wireless tracking device 122 remains within the geofence 410 is stored and then transmitted to the remote monitoring station 128 when the wireless tracking device 122 leaves the geofence 410. Fig. 4, the region 420 represents an area in which wireless communication of the wireless tracking device 122 is available with good reception.

[0040] In the example of Fig. 4, the wireless tracking device 122 moves from point X to point Z. While the wireless tracking device 122 is in the region 420 and away from the geofence 410 (represented by the line XY), the wireless tracking device 122 switches to active mode at a first frequency (i.e., sampling rate). As the wireless tracking device 122 approaches the geofence 410 (represented by the line YZ), the wireless tracking device 122 switches to active mode at a second frequency that is higher than the first frequency (i.e., the wireless tracking device 122 switches to active mode more frequently). For example, as the wireless tracking device 122 moves from point X to point Y, the wireless tracking device 122 may switch from sleep mode to active mode every 10 minutes.The same wireless tracking device 122 may switch from sleep mode to active mode every 5 minutes when the wireless tracking device 122 moves from point Y to point Z.

[0041] In one embodiment, the wireless tracking device 122 switches to active mode at a gradually increasing frequency or remains in active mode for an extended period of time as the wireless tracking device 122 approaches the geofence 410.

[0042] Fig.Figure 5 shows a flowchart of the process of switching between active mode and sleep mode when the geofence is implemented. In the first step, 508 switches the wireless tracking device 122 to active mode. In active mode, the low-power system controller 214 determines 510 the position, direction of travel, and speed of the wireless tracking device 122. Based on the position, direction of travel, and speed of the wireless tracking device 122, the wireless tracking device 122 calculates 514 the estimated time when the wireless tracking device 122 will arrive at the region of the geofence 410.

[0043] Based on the estimated time of arrival at the geofence region 410, the interval at which the active mode is switched is determined 518. After all processes in the current active mode have been completed or after a preset time to remain in the active mode has elapsed, the wireless tracking device 122 switches 522 to sleep mode.

[0044] The wireless tracking device 122 then determines 526 whether it is time to switch to active mode based on the calculated interval. If it is time to switch to active mode, the process continues to switch the wireless tracking device 122 to active mode 508 and repeats the subsequent steps. If it is not yet time to switch to active mode, the wireless tracking device 122 remains in sleep mode.

[0045] By adjusting the interval at which the wireless tracking device 122 is switched to sleep mode based on the estimated time of arrival at an area of ​​poor wireless signal reception, the wireless tracking device 122 can continue to update the remote monitoring station 128 with wireless messages without excessive power consumption.

Claims

[1] A wireless tracking device (122) comprising: a location determining device configured to determine a geographical position of the wireless tracking device (122); at least one sensor (250, 254, 258, 262) configured to generate a sensor signal representative of a condition or characteristic associated with the wireless tracking device (122); at least one controller (210, 214) coupled to the location determining device and the at least one sensor (250, 254, 258, 262), wherein the at least one controller (270, 272) is configured to: generate a message indicating the geographical position, condition, or characteristic associated with the wireless tracking device (122); placing the wireless tracking device (122) in a first mode; and switching the wireless tracking device (122) to a second mode that consumes more power than the first mode in response to a sensor signal representing a predefined event; and a communication module (226) configured to send the message over a wireless network, wherein the at least one controller (210, 214) is further configured to: calculate (514) an estimated time of arrival of the wireless tracking device at a geographic region (410) where the message should not be sent over the wireless network; determine an interval to switch the wireless tracking device (122) from the first mode to the second mode (518); and to determine whether to switch to the second mode based on the specified interval. [2] The wireless tracking device (122) of claim 1, wherein the at least one controller (210, 214) comprises a first controller (214) and a second controller (210) that consumes more power during operation than the first controller (214). [3] The wireless tracking device (122) of claim 2, wherein the first controller (214) is configured to receive sensor signals from a plurality of sensors (250, 254, 258, 262), and wherein the second controller (210) is configured to operate the location determining device and the communication module (226). [4] The wireless tracking device (122) of claim 3, wherein the first controller (214) is configured to turn off the second controller (210), the location determining device, and the communication module (226) in the first mode. [5] The wireless tracking device (122) of claim 1, further comprising a limited power source (234) to power the location determining device, the at least one controller (214) and the communication module (226). [6] The wireless tracking device (122) of claim 1, wherein the location determining device comprises a Global Positioning System (GPS) module (222). [7] The wireless tracking device (122) of claim 6, wherein the location determining device receives ephemeris data from a remote server via the wireless communication module (226). [8] The wireless tracking device (122) of claim 1, wherein the interval is shortened as the wireless tracking device (122) approaches the geographic region. [9] The wireless tracking device (122) of claim 1, wherein the at least one controller (210, 214) is configured to: maintaining the wireless tracking device (122) in the second mode in response to receiving the sensor signal with a change that exceeds a first threshold; and switching the wireless tracking device (122) from the first mode to the second mode in response to receiving the sensor signal with a change that exceeds a second threshold that is higher than the first threshold. [10] The wireless tracking device (122) of claim 1, wherein the at least one sensor (250, 254, 258, 262) comprises an accelerometer (250). [11] A method of operating a wireless tracking device (122), comprising: placing the wireless tracking device (122) in a first mode; generating a sensor signal representing a condition or characteristic associated with the wireless tracking device (122); switching the wireless tracking device (122) to a second mode that consumes more power than the first mode in response to a sensor signal representing a predefined event; determining a geographical position of the wireless tracking device (122); generating a message indicating the geographical position, condition, or characteristic associated with the wireless tracking device (122); sending the message over a wireless network; calculating (514) an estimated time of arrival of the wireless tracking device at a geographic region (410) where the message should not be sent over the wireless network; determining (518) an interval to switch the wireless tracking device (122) from the first mode to the second mode; and determine whether to switch to the second mode based on the specified interval. [12] The method of claim 11, comprising turning off one of two controllers (210, 214), a location determining device of the wireless tracking device (122) and a communication module (226) to send the message in a first mode. [13] The method of claim 11, wherein the position is determined by a Global Positioning System (GPS). [14] The method of claim 13, further comprising receiving ephemeris data from a remote server via the wireless communication module (226). [15] The method according to claim 11, further comprising: calculating an estimated time of arrival of the wireless tracking device (122) at a geographic region (410) where the message should not be sent over the wireless network; determining an interval to switch the wireless tracking device (122) from the first mode to the second mode; and determine whether to switch to the second mode based on the specified interval. [16] The method of claim 15, wherein the interval is shortened as the wireless tracking device (122) approaches the geographic region (410). [17] The method according to claim 11, further comprising: maintaining the wireless tracking device (122) in the second mode in response to receiving the sensor signal with a change that exceeds a first threshold; and switching the wireless tracking device (122) from the first mode to the second mode in response to receiving the sensor signal with a change that exceeds a second threshold that is higher than the first threshold. [18] The method of claim 11, wherein the sensor signal is generated by an accelerometer (150). [19] A computer-readable storage medium structured to store instructions executable by a processor in a wireless tracking device (122), the instructions, when executed, causing the processor to: placing the wireless tracking device (122) in a first mode; generating a sensor signal representative of a condition or characteristic associated with the wireless tracking device (122); switching the wireless tracking device (122) to a second mode that consumes more power than the first mode in response to a sensor signal representing a predefined event; determine a geographical position of the wireless tracking device (122); generate a message indicating the geographical position, condition, or characteristic associated with the wireless tracking device (122); send the message over a wireless network; calculate (518) an estimated time of arrival of the wireless tracking device at a geographic region (410) where the message should not be sent over the wireless network; determine an interval to switch the wireless tracking device (122) from the first mode to the second mode (514); and to determine whether to switch to the second mode based on the specified interval.

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