Abstract: The detection of a microphone within a selected site includes broadcasting an acoustic signal having two components with different frequencies selected to produce the re-broadcast, by a microphone in the broadcast field, of a selected resonant responsive signal, and sensing the re-broadcast of such a responsive signal. Determining the direction in which such a responsive signal is sensed determines the location of a microphone detected to be present within the selected site.

Abstract: An anti-theft lock arrangement for a motor vehicle comprises a lock mechanism that normally disables the motor vehicle and a timing mechanism, actuated when the ignition switch is switched to a first position, for transmitting a lock release signal to unlock the locking device after a predetermined time interval from the instant of actuation of the timing mechanism, the locking mechanism being unlocked only when the lock release signal is applied thereto and the ignition switch is switched to a second position after the time interval and during the duration of the lock release signal, neither the predetermined time interval nor the lock release signal being capable of being sensibly perceived.