Abstract: An infra-red remote personal alarm system consists of a portable transmitter unit (10) which is intended to be worn or to be manually carried by the user, and which is operable by the user at any particular location to transmit an alarm signal in an emergency and which is to be received by a central receiving station (41) so that appropriate action can be initiated in response thereto. The transmitter unit is electrically operable and includes means (15) for transmitting pulsed infra-red alarm signals which can be picked-up by an infra-red signal receiver at the location of the user, and then retransmitted as an oscillating electrical signal via direct wiring (38, 39, 40, 42, 43) to the central receiving station (41) as a warning signal indicative at location monitoring points (43, 44) of the location from which the emergency call has been made.