Abstract: A device for controlling a security device, preferably for securing a motor vehicle against unauthorized use, a portable key having a transmitter for sending messages after every actuation and the security device comprising a receiver for messages and the messages including alternating code values which change from message to message. A lag time of equal duration is implemented in the transmitter and receiver respectively, such that the transmitter is switched off by the duration of the lag time. When the transmitter which is not switched off is actuated, a message is transmitted, and when the switched-off transmitter is actuated the transmitter is switched on. The security device is controlled if the time difference information included in the message corresponds to the time difference information which is correspondingly determined in the receiver.

Abstract: In a device for controlling a security device, preferably for securing a motor vehicle against unauthorized use, a portable key having a transmitter for sending messages after every actuation and the security device comprising a receiver for messages and the messages including alternating code values which change from message to message, there is provision that a lag time of equal duration is implemented in the transmitter and receiver respectively, that the transmitter is switched off by the duration of the lag time after a respective last actuation that, when the transmitter which is not switched off is actuated a message is transmitted which contains information (time difference information) indicating how much time has passed since the preceding message was transmitted, that when the switched-off transmitter is actuated the transmitter is switched on and transmits a message which includes, as time difference information, information indicating that the lag time has expired, and that the security device is