Sound activated transmitter

摘要

A remote annunciator system in which the emission of an acoustic signal by a first annunciator is detected by an acoustic signal detector which causes a radio frequency transmitter to transmit a radio frequency signal. A radio frequency receiver which receives the signal operates a second annunciator which is remote from the first annunciator, to cause the second annunciator to emit an audible or visual signal. Preferably, the radio frequency signal is encoded and is decoded at the receiver, and if the first annunciator can emit two different accoustic signals, the transmitted signal is encoded dependent upon which acoustic signal is emitted and the receiver decoder causes the second annunciator to emit an audible signal or a visual signal which depends on the transmitted signal encoding.