Abstract: A security system for consumer equipment has a lock for preventing use of the equipment, and broadcasts a beacon signal indicating stolen status, if the lock does not receive a valid key signal over a wireless link. The beacon signal can help police identify stolen goods, and makes mere possession of stolen goods more risky and so deters theft. The lock serves to make the equipment useless or very expensive to make useful, once stolen. Little or no change of behaviour by users is needed. The beacon can be passive, in snooze state to save power, with periodic listening for an interrogating (police) radio, which causes it to wake up and transmit. The system can securely store, and optionally broadcast, a secure identifier which is traceable to an owner of the equipment, to aid recovery and conviction. Tamper resisting measures can be included.

Abstract: A frequency synthesizer including an oscillator (1) whose frequency is controlled by a tuning signal (TS), a phase detector (4) and a phase lock loop circuit (5, 6). A tuning indicator (7) has a tolerance on the phase difference between the tuning frequency signal and the reference frequency signal. The phase detector produces a first (PS1) and a second (PS2) phase signal upon leading and lagging, respectively, of the phase between the tuning frequency signal (F.sub.T) and a reference frequency signal (F.sub.R). The tuning indicator includes delay circuits provided at the input of AND-gates in such manner as to cancel the phase signals (PS1) and (PS2) of a duration less than a predetermined duration, and a register producing a confirmed tuning indication signal (IS) only when the phase signals (PS1) and (PS2) indicate stable tuning during at least two consecutive periods of the reference frequency (F.sub.R).