Handheld device for controlling motor vehicle

Abstract

The invention relates to a method (300) for positioning a handheld device (110) relative to a motor vehicle (105), comprising the following steps: agreeing a time interval between the handheld device (110) and the motor vehicle (105); transmitting a series of wireless pulses between the motor vehicle (105) and the handheld device (110); the wireless pulses are emitted in a staggered manner at the time intervals; and determining a position of the handheld device (110) relative to the motor vehicle (105) on the basis of a time interval between the reception times of the wireless pulses on the handheld device (110). The time interval is agreed according to a power capability of an energy source (155) of the handheld device (110).

Description

Technical Field

[0001] The present invention relates to the control of a motor vehicle. In particular, the present invention relates to the control of a motor vehicle by means of a handheld device. Background Art

[0002] A motor vehicle comprises a control device which is provided for controlling safety functions of the motor vehicle, such as opening or closing the motor vehicle or activating or deactivating an anti-theft lock. For the control, a wirelessly communicating handheld device can be used, which can be integrated into a mechanical key or implemented in the form of a key fob. When the handheld device is operated, messages can be exchanged between the handheld device and the motor vehicle in order to implement the safety functions. Handheld devices which are specially provided for communication with the motor vehicle usually use low-frequency (125 kHz) or high-frequency (434 MHz) radio technology.

[0003] Mobile devices (smartphones) can also be used to wirelessly control the safety functions of a motor vehicle. The radio technologies used here include Bluetooth Low Energy (BLE) with a frequency of approximately 2.4 GHz and Ultra Wideband (UWB) with a frequency range of approximately 6 to 10 GHz. Preferably, the two radio technologies are used interchangeably to enable reliable communication on the one hand and to determine the position of the mobile device relative to the motor vehicle on the other hand. In this case, significantly further security concepts can be implemented than can be achieved with dedicated handheld devices. The control can be implemented, for example, according to the standard published by the Car Connectivity Consortium, which is known as the digital car key.

[0004] In order to be able to use the motor vehicle even without a mobile phone, the handheld device should be equipped with the technology of a mobile device. In order to be able to implement the handheld device in a small and light manner, the size of the energy source of the handheld device is designed to be as small as possible. In a known method for locating a handheld device relative to a motor vehicle by means of UWB, a strong load on the energy source can occur during the reception of a series of radio pulses. The energy source can, for example, include a button cell, which should only withstand a low current load of approximately 10 to 15 mA, while during the reception period a significantly higher current of, for example, approximately 130 mA can be consumed briefly.

[0005] The pulse-shaped energy consumption can be evened out by using capacitors. If the button cell is in good condition, there are no problems with receiving the radio pulse train. But if the button cell is operating under suboptimal conditions, for example because it is partially discharged or low temperatures are present, the voltage supplied to the handheld device can briefly drop below a predetermined threshold value during reception, which can disrupt processing. Summary of the invention

[0006] The object of the present invention is to provide an improved technology for communication between a handheld device and a motor vehicle. The invention achieves this object by means of the subject matter of the independent claims.

[0007] According to a first aspect of the present invention, a method for locating a handheld device relative to a motor vehicle comprises the following steps: agreeing on a time interval between the handheld device and the motor vehicle; transmitting a series of radio pulses from the motor vehicle to the handheld device; emitting the radio pulses at the time intervals staggered from different locations on the motor vehicle; and determining the position of the handheld device relative to the motor vehicle based on the time intervals between the reception times of the radio pulses on the handheld device. The time intervals are agreed on as a function of the power capability of an energy source of the handheld device.

[0008] This prevents the energy source from being so heavily loaded during the reception of the radio pulses that it negatively affects the function of other components of the handheld device. This increases the functional reliability of the handheld device. Even under unfavorable conditions, the handheld device can operate better and more reliably.

[0009] Preferably, the time interval is extended as the power capacity of the energy source decreases. If the power capacity of the energy source is high, the time interval can be selected to be short and, for example, about 1.333 ms. If the power capacity of the energy source is only medium, the time interval can be increased to an average length of, for example, about 2.667 ms. If the power capacity of the energy source is at the lower end of the available interval, the time interval can be increased to a long time of, for example, 4.00 ms. Typically, during positioning, a series of pulses as many as the transmitting devices present at different locations of the motor vehicle are transmitted. The number of transmitting devices is usually in the single digit, so that even in the case of long time intervals, no noticeable delay relative to the short time intervals can be determined by the person operating the handheld device.

[0010] In one embodiment, the energy source provides a voltage, wherein the power capability is determined as a function of the provided voltage. In other words, the voltage of the energy source can be used as an indicator for the state of charge (SoC). If the energy source is not significantly loaded by consumers, the voltage is preferably determined as a no-load voltage. In particular, if the energy source comprises an electrochemical energy storage device and is implemented as a battery or a battery, the voltage can indicate the state of charge in a good approximation. The higher the state of charge, the greater the power capability of the energy source can be.

[0011] In embodiments in which the energy source provides a voltage, the power capability can be determined based on the internal resistance of the energy source. The lower the internal resistance, the greater the power capability can be. The internal resistance can be determined by connecting an electrical consumer to the energy source and determining the current flowing through the consumer based on the voltage applied to the consumer. The consumer can include, in particular, a transmitter or a receiver of a handheld device.

[0012] If the energy source comprises an electrochemical energy store, the power capacity can be determined as a function of the temperature in the region of the energy store. The lower the temperature, the lower the power capacity can be. It is conceivable that batteries and accumulators may be negatively affected in terms of their power capacity when they are used at low temperatures. The temperature in the region of the energy source can be determined simply, for example, by means of temperature-dependent components such as diodes.

[0013] If the energy source comprises an energy storage, the power capability of the energy storage can be determined based on the energy that has been extracted from the energy storage in the past. The energy storage is non-renewable, so that only a predetermined amount of energy can be extracted from the energy storage. A model can be constructed for the energy that can still be extracted from the energy storage. The more often energy is extracted from the energy storage or the more energy is extracted, the less energy can remain in the energy storage. In other words, the more energy has been extracted from the energy storage, the lower the power capability of the energy storage can be. Such good models are known in particular for accumulators and batteries.

[0014] A handheld device for communicating with a motor vehicle comprises a wireless transceiver, an energy source, and a processing device. The processing device is configured to negotiate a time interval with the motor vehicle, receive a series of wireless pulses that are emitted from different locations on the motor vehicle at staggered intervals, and determine the position of the handheld device relative to the motor vehicle based on the time interval between the reception times of the wireless pulses on the handheld device. The processing device is configured to negotiate the time interval based on the power capability of the energy source of the handheld device.

[0015] The technology proposed in this article can be used both for pulse transmission from the motor vehicle to the handheld device and in the opposite direction. The transceiver comprises a transmitter and a receiver. If only the direction from the handheld device to the motor vehicle is to be covered, only a transmitter can be provided instead of the transceiver. If only the proposed technology is to be provided for transmission from the motor vehicle to the handheld device, only a receiver can be used in a corresponding manner instead of the transceiver. This article focuses on the transceiver in a generalized manner; this means that it can be reduced to a transmitter or a receiver.

[0016] The processing device is preferably also provided for determining the current power capacity of the energy source. The method described herein can be implemented partially or completely by means of a handheld device and in particular by means of a processing device. For this purpose, the processing device can be implemented electronically and, for example, include an integrated circuit, a programmable logic module or a programmable microcomputer. The method can be implemented in the form of a configuration or as a computer program product with program code means for the processing device. The configuration or computer program product can be stored on a computer-readable data carrier. The features or advantages of the method can be transferred to the device or vice versa.

[0017] In one embodiment, the transceiver is activated only when a radio pulse is expected to arrive or a pulse is to be sent. During the activation of the transceiver, the voltage of the energy source can drop. In order to prevent the voltage from dropping to such an extent during the sending or receiving of the radio pulses that the function of the processing device is negatively affected, the time interval can be extended. The energy extracted from the energy source during the sending or receiving of the series of pulses can remain unchanged by extending the time interval, but the load can be distributed over a larger period of time. In this way, short-term drops in the voltage of the energy source can be prevented.

[0018] Preferably, the energy source comprises a buffer store in order to provide the increased current for a short time. The buffer store can be implemented in particular as a capacitor. The capacitor also helps to reduce the short-term load of the energy source. As a result, the energy source can bear the load more evenly.

[0019] In one embodiment, the processing device is configured to extend the time interval if the voltage of the energy source falls below a predetermined threshold value during activation of the wireless transceiver. In other words, it can be determined whether the voltage of the energy source has dropped inadmissibly during the transmission or reception of the series of pulses. If this is the case, the time interval can be extended to prevent the voltage from dropping too sharply again. When the energy source is charged or replaced, the time interval can be set to a short value again.

[0020] The handheld device may include a reset generator to place the processing device in a predetermined state when the voltage is below a predetermined threshold. The reset generator may be implemented together with the processing device, for example as an integrated circuit or a microcontroller. It is common to use a reset generator on a digital processing device. The reset generator may be used to detect an undervoltage condition that is harmful or disruptive to the operation of the processing device.

[0021] It is further preferred that the handheld device comprises a further wireless interface for communicating with the motor vehicle. The described wireless transceiver can be part of a first wireless interface, in particular operating with the aid of UWB technology. The further wireless interface can, for example, operate according to the Bluetooth standard, in particular Bluetooth Low Energy (BLE). Both interfaces can operate according to a predetermined protocol in order to communicate between the handheld device and the motor vehicle. Preferably, the handheld device executes a known protocol here. The protocol can be contained in particular by the digital car key.

[0022] The communication standard implemented by the handheld device may specify a maximum or minimum time interval for communication between the handheld device and the motor vehicle. In one embodiment, such limits may be exceeded or undershot to implement the techniques described herein and prevent the handheld device from failing to locate the motor vehicle when the power source power capability of the handheld device is insufficient.

[0023] Particularly preferably, the handheld device is configured to control functions of the motor vehicle based on information exchanged with the motor vehicle. In particular, the handheld device can perform a bilateral authentication with the motor vehicle and request a predetermined function of the motor vehicle. The functions can include, for example, unlocking, opening or releasing a driving function of the motor vehicle. The handheld device is preferably implemented as a dedicated device, which cannot be used for other purposes except for communicating with the motor vehicle. Nevertheless, the handheld device can still work similarly to a mobile device (smartphone) in terms of controlling the functions of the motor vehicle, and the mobile device can also perform other functions in addition. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will now be described in more detail with reference to the accompanying drawings, which are as follows:

[0025] Figure 1 Showing the system;

[0026] Figure 2 shows an exemplary voltage variation curve on a handheld device; and

[0027] Figure 3 A flow chart showing the method is shown. DETAILED DESCRIPTION

[0028] Figure 1A system 100 is shown, which includes a motor vehicle 105 and a handheld device 110. A control device 115 is provided on the motor vehicle 105, which is provided for communicating with the handheld device 110 and controlling the functions of the motor vehicle 105. The functions may include safety functions, such as locking or unlocking an interlock (Zugriffssperre). The control device 115 includes a processing device 120, a plurality of wireless interfaces 125, and another wireless interface 130. The interface 125 usually includes a transceiver as a combination of a transmitter and a receiver. The transmitter and the receiver may also be constructed separately from each other. Strictly speaking, the communication on the motor vehicle 105 side is always carried out by means of the control device 115, and in the following, it is also simplified to say that the handheld device 110 communicates with the motor vehicle 105.

[0029] Interfaces 125 are mounted at various locations on motor vehicle 105 and can each include an antenna. Figure 1 The position of the interface 125 shown in the figure is to be understood as exemplary. Preferably, the interface 125 can be used to send and receive UWB signals in the frequency range of about 6 to 10 GHz. The further wireless interface 130 may include one or more further dedicated antennas. The wireless interface 130 preferably operates at a frequency of about 2.4 GHz using BLE technology.

[0030] The handheld device 110 comprises a processing device 140, at least one wireless interface 145, preferably operating according to UWB technology, and preferably a further wireless interface 150, preferably operating according to BLE technology. The wireless interface 145 is preferably provided both for sending UWB signals and for receiving UWB signals. The interface 150 is provided for communicating with the interface 130 of the control device 115 on the motor vehicle 105.

[0031] The handheld device 110 preferably comprises an energy source 155, which is further preferably embodied as an energy storage device 155 and in particular as an electrochemical energy storage device 155. For example, the energy source 155 can comprise an accumulator or a battery. Optionally, a buffer storage device 160 is provided in order to smooth the time profile of the energy extracted from the energy source 155. The buffer storage device 160 preferably comprises a capacitor and can be decoupled from the energy source 155, for example by means of a diode.

[0032] The voltage monitoring device 165 can determine whether the voltage provided by the energy source 155 or the voltage provided to the components of the handheld device 110 has dropped below a predetermined threshold value. In this case, a signal can be provided to the processing device 140, which signal includes a reset signal in one embodiment to reset the processing device 140 to a predetermined state, so that the voltage monitoring device 165 can also be referred to as a reset generator 165. By providing the reset signal, the processing of the processing device 140 can be interrupted or stopped. The voltage monitoring device 165 can also include an analog-to-digital converter, by means of which the processing device 140 can actively determine the voltage of the energy source 155 or the buffer memory 160. The determined voltage can be numerically compared with a predetermined threshold value.

[0033] Figure 1 A user interface, such as a button or a keyboard, is not shown, by means of which a person can activate the handheld device 110. The activation can trigger a predetermined communication between the handheld device 110 and the motor vehicle 105. The communication may include mutual authentication, which may be based on an asymmetric encryption key. In addition, the distance and / or direction of the handheld device 110 relative to the motor vehicle 105 may be determined.

[0034] The communication and the determination of the distance or direction can be performed by means of different wireless technologies. These technologies can be used in combination or interleaved with each other to achieve an orderly signal exchange process. For example, the communication between the motor vehicle 105 and the handheld device 110 can be performed according to the provisions of the digital car key in principle as follows:

[0035] The transmission of information via BLE by means of interfaces 130 and 150 in order to configure the communication by means of UWB interfaces 125 , 145 .

[0036] The motor vehicle 105 sets all UWB interfaces 125 to the receiving state.

[0037] - Handheld device 110 sends a pre-poll.

[0038] - Handheld device 110 sends a poll.

[0039] - The first UWB interface 125 sends a response. The handheld device 110 is here in a receiving state.

[0040] - Other UWB transmitting devices 125 send responses in turn. The handheld device 110 is in a receiving state here.

[0041] - Handheld device 110 sends the final packet.

[0042] - The handset 110 sends the final data packet (Final_Data packet).

[0043] The individual UWB packets are transmitted in short sequences. A typical configuration is to send a packet every T_Slot=2.667ms (N_Chap_per_Slot=8). The slot times are determined or agreed upon in advance between the handheld device 110 and the vehicle. The vehicle 105 can determine the distance between the handheld device 110 and the vehicle anchor from the signal propagation time and thus determine the position.

[0044] Figure 2 In the lower area, exemplary voltage profiles are shown at the receiving device 145 and the processing device 140 of the handheld device 110. In the horizontal direction, the time is given in seconds and in the vertical direction, the voltage is given in volts. If the power capacity of the energy source 155 is high, a first profile 205 can be obtained; the second profile 210 is associated with an energy source 155 with a medium or low power capacity. It should be noted that the profiles 205, 210 are shown schematically and qualitatively.

[0045] The upper region shows messages exchanged between handheld device 110 and motor vehicle 105. Messages are represented by arrows that extend in the transmission direction from handheld device 110 to motor vehicle 105 or vice versa. The horizontal position of the arrows corresponds to the time of the message in the voltage curve diagram.

[0046] With reference to first curve 205 , the no-load voltage of energy source 155 is approximately 2.8 V. If the voltage at processing device 140 and / or receiving device 145 falls below a predetermined threshold value, here exemplarily 1.8 V, an undervoltage can be detected, in which case processing device 140 is reset to a predetermined state (reset).

[0047] In order to determine the distance or position of the handheld device 110 relative to the motor vehicle 105, a series of pulses are usually exchanged between the motor vehicle 105 and the handheld device 110. These pulses each have a predetermined time duration, and each pulse is separated from the previous or subsequent pulse by a predetermined time interval. The pulses are successively emitted by different transmitting devices 125 of the motor vehicle 105.

[0048] The propagation speed of the emitted radio pulses corresponds essentially to the speed of light. Since the transmitting devices 125 are located at different locations on the motor vehicle 105, the distances that the individual pulses must travel to reach the receiving device 145 of the handheld device 110 vary. Accordingly, the time intervals between the reception times of temporally successive pulses on the handheld device 110 usually differ from the predetermined time intervals between the pulses during emission. The relative distances between the receiving device 145 and different transmitting devices 125 can be determined from the deviations in the relative time differences between the reception times and the time intervals.

[0049] The operation of the receiving device 145 generally requires that a significant amount of energy be drawn from the energy storage 155. In other words, an increased current can be drawn from the energy storage 155 during reception. Due to the finite internal resistance of the energy source 155, the voltage of the energy source 155 drops when the receiving device 145 is switched on. If a capacitor 160 is provided, this effect can be mitigated. Figure 2 The point in time at which receiving device 145 is switched on is indicated by the almost vertically descending sections of curves 205 , 210 .

[0050] Since it is approximately known when the emitted pulse is expected to be received, the receiving device 145 is preferably operated only within such a time range. Between these times, the receiving device 145 is turned off so that the voltage of the energy source 155 can rise again. The rise is usually carried out more slowly than the fall.

[0051] The multiple loading of the energy source 155 by the series of pulses generally results in a drop in the average voltage provided. This is not critical for the first profile 205, since the voltage does not approach the threshold value of 1.8 V at any point in time.

[0052] However, it may happen that, with respect to the second variation curve 210, the voltage of the energy source 155 drops below a predetermined threshold value at least briefly. In the example shown, this is the case at time 0.045. A brief undershoot of the threshold value of 1.8 V may be sufficient to trigger the reset generator 165. This may prematurely terminate the distance or position determination.

[0053] It is proposed that if the power capacity of the electrical energy store 155 is not sufficient to reliably prevent the described undershooting of the threshold value, the time interval between the emission of two successive pulses is increased. The time range in which the receiving device 145 is switched on can then be corrected in time to a corresponding extent. The energy store 155 can have a better chance of regenerating between the loads caused by the receiving device 145 and of increasing the voltage provided by the energy store.

[0054] Figure 3 A flow chart of an exemplary method 300 is shown. The method 300 can be carried out in particular by means of the system 100 .

[0055] In step 305, preparations can be made for positioning the handheld device 110 relative to the motor vehicle 105. For this purpose, information can be exchanged between the handheld device 110 and the motor vehicle 105 accordingly. Preferably, the data exchange takes place by means of the further interfaces 130, 150. In one embodiment, preparations can be made for positioning when the handheld device 110 is within the communication range of the interfaces 130, 150, but not yet within the communication range of the interfaces 125, 145. The actual positioning can only be carried out when the handheld device 110 is close enough to the motor vehicle 105 so that radio pulses can be exchanged between the transmitters 125 and 145.

[0056] In step 310, the power capability of the energy source 155 can be determined on the handheld device 110 side. The power capability can indicate to what value the voltage provided by the energy source 155 drops when the receiving device 145 is turned on for a predetermined duration. The higher the voltage, the greater the power capability can be. To determine the power capability, it can be considered which voltage the energy source 155 provides directly before the receiving device 145 is turned on.

[0057] The power capability can be determined based on different approaches. In one embodiment, the parameters of the energy source 155 can be determined in step 315. The parameters can include, in particular, no-load voltage, internal resistance or temperature. The power capability can then be determined based on one or more of the proposed parameters of the energy source 155.

[0058] In step 320, it can be determined whether the energy source 155 was overloaded when the position of the handheld device 110 relative to the motor vehicle 105 was determined in the past. If the voltage provided by the energy source 155 is below a predetermined threshold, an overload can be determined. In this case, the time interval used in the past positioning can be extended. The extension can be performed in predetermined increments. If it is determined at a later point in time that the energy source 155 has been recharged or replaced, the time interval can be reset to a predetermined low value.

[0059] In step 325, the power capability of the energy source 155 may be determined based on the model. The model may be based on a predetermined amount of energy stored in or available from the energy source 155. The extraction of energy from the energy source 155 may be tracked and the remaining or extractable energy may be determined based on the model. The more energy remaining, the greater the power capability of the energy source 155 may be. It is noted that the power capability of the energy source 155 may be determined based on one or more of steps 315 to 325 or a portion thereof.

[0060] In step 330, a time interval can be agreed between the handheld device 110 and the motor vehicle 105. In this case, the handheld device 110 proposes one or more time intervals of different lengths, wherein the shortest time interval is preferably long enough to avoid overloading the energy source 155 when determining the position. If step 320 has been previously performed, the shortest time interval provided can correspond to the time interval determined in step 320. The motor vehicle 105 can confirm one of the time intervals provided, so that both parties 105, 110 know which time interval to use for positioning.

[0061] In step 335 , wireless pulses may be emitted alternately by handheld device 110 and motor vehicle 105 . The pulses are emitted in sequence, with a time interval being present between successive pulses. Preferably, the pulses are emitted by different ones of transmitters 125 and 145 .

[0062] In step 340, radio pulses can be received by handheld device 110 and motor vehicle 105. For this purpose, receiving devices 125 and 145 can each be briefly activated when an incoming radio pulse is expected.

[0063] In step 345, the direction and / or distance of handheld device 110 relative to motor vehicle 105 can be determined. For this purpose, the relative time intervals between the reception times of the transmitted radio pulses can be taken into account. With knowledge of the geometry of the location at which transmitting device 125 is installed in motor vehicle 105, the distance and / or direction of handheld device 110 relative to motor vehicle 105 can be determined.

[0064] Reference numerals list

[0065] 100 systems

[0066] 105 Motor Vehicles

[0067] 110 Handheld Devices

[0068] 115 Control Equipment

[0069] 120 Processing device

[0070] 125 Transmitter

[0071] 130 interface

[0072] 140 Processing device

[0073] 145 receiving device

[0074] 150 interfaces

[0075] 155 Energy source, energy storage

[0076] 160 Buffer memory

[0077] 165 Voltage monitoring device, reset generator

[0078] 205 First Change Curve

[0079] 210 Second change curve

[0080] 300 Methods

[0081] 305 Preparing for Positioning

[0082] 310 Determine the power capability of the energy source

[0083] 315 Determine the parameters of the energy source

[0084] 320 on reset: Extend the time interval

[0085] 325 Energy Source Model

[0086] 330 Agreement Time Interval

[0087] 335 emits pulses at time intervals

[0088] 340 receiving pulse

[0089] 345 Positioning Handheld Device

Claims

1. A method (300) for positioning a handheld device (110) relative to a motor vehicle (105), the method (300) comprising the following steps: - agreeing (330) a time interval between the handheld device (110) and the motor vehicle (105); - exchanging (335, 340) a series of wireless pulses between the motor vehicle (105) and the handheld device (110); - the wireless pulses are emitted from the handheld device (110) and from different locations on the motor vehicle (105) at staggered intervals of time; and - determining (345) the position of the handheld device (110) relative to the motor vehicle (105) based on the time intervals between the reception times of the radio pulses at the handheld device (110); The invention is characterized in that the time interval is agreed upon according to the power capability (310) of the energy source (155) of the handheld device (110).

2. The method (300) according to claim 1, wherein: The time interval is extended as the power capability of the energy source (155) decreases.

3. The method (300) according to claim 2, wherein: The energy source (155) provides a voltage and determines a power capability based on the provided voltage.

4. The method (300) according to any one of the preceding claims, wherein: The energy source (155) provides a voltage and the power capability is determined according to the internal resistance of the energy source (155).

5. The method (300) according to any one of the preceding claims, wherein: The energy source (155) comprises an electrochemical energy storage device; and the power capacity is determined as a function of the temperature in a region of the energy storage device.

6. The method (300) according to any one of the preceding claims, wherein: The energy source (155) comprises an energy storage device and determines a power capability of the energy storage device based on energy extracted from the energy storage device in the past.

7. A handheld device (110) for communicating with a motor vehicle (105), the handheld device (110) comprising: - Wireless receiver; - Energy Source (155); and - a processing device (140) configured to: - agreeing on a time interval with the motor vehicle (105); - receiving a series of radio pulses, which are emitted from different locations on the motor vehicle (105) at staggered intervals at the time intervals; and - determining the position of the handheld device (110) relative to the motor vehicle (105) based on the time intervals between the reception times of the radio pulses at the handheld device (110); It is characterized in that - The processing device (140) is further configured to negotiate the time interval according to the power capability of the energy source (155) of the handheld device (110).

8. The handheld device (110) according to claim 7, wherein: The receiver is activated only when a radio pulse is expected to arrive; the voltage of the energy source (155) is reduced during the activation of the receiver.

9. The handheld device (110) according to claim 7 or 8, wherein: The energy source (155) comprises a buffer store (160) in order to provide an increased current for a short period of time.

10. The handheld device (110) according to any one of claims 7 to 9, wherein: If the voltage of the energy source (155) is below a predetermined threshold during activation of the wireless receiver, the time interval is extended.

11. The handheld device (110) of claim 10, further comprising a reset generator (165) to place the processing device (140) in a predetermined state when the voltage is below a predetermined threshold.

12. The handheld device (110) according to any one of claims 7 to 11, further comprising a further wireless interface (150) for communicating with a motor vehicle (105).

13. The handheld device (110) according to any one of claims 7 to 12, wherein: The handheld device (110) is configured to perform a two-way authentication with a motor vehicle (105); and request a predetermined function of the motor vehicle (105).

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