Abstract: A signalling device to be worn on the person includes an emergency button (2) which triggers an internal transmitter to transmit an encoded identification signal followed by audio signals derived from sounds picked up by a microphone (3). The transmitted signals are picked up by a control box (21) containing a radio receiver which encodes the signals and commands an alarm box (24) to send out an audible and/or visual warning. Such warnings alternate with periods in which the alarm box broadcasts sounds picked up by the microphone (3).