Abstract: The invention relates to a method for determining the perpendicular distance between an object and a device whose position varies, in particular a motor vehicle, in the case of which device a first sensor which is arranged on this device emits a signal which is reflected by the object, and this reflected signal is received by this first sensor, in which case the delay time of the signal from transmission to reception is used by the first sensor to determine the distance between the first sensor and the object.

Abstract: In an apparatus and a method for enabling and/or activating/deactivating a security device, in particular an access device for a motor vehicle, in which, after receiving a stimulation sequence which is transmitted by a transmitter of a transmission device, coded information (enable signal) is transmitted by a portable transmission unit (radio key) and is received by a receiver in the transmission device, a controller comparing the received enable signal with predetermined coded information and, if they match, emitting an actuation signal to the security device, if a plurality of matching radio keys are present in the reception area of the device, the transmission quality between the security device and the radio keys is checked. The only radio key which is used to transmit an enable signal is that which has the best transmission conditions to the security device.

Abstract: A system and method for determining the distance between an object and a device of varying location, in which a first or second sensor arranged on the device emits a signal which is reflected by the object. The reflected signal is received by the sensor transmitting the signal and by the respective other sensor, and an evaluation device determines the propagation times between the transmission of the signal and the reception of the signal for each sensor and determines therefrom all the possible positions of the objects relative to the device of varying location referred to the sensor. The distance from the motor vehicle being determined from the corresponding positions of the measurements.