Battery economizing in communication system

In communications systems such as telemetry systems in which a receiver ( 34 ) is periodically energised to receive transmissions from a central station, the receiver includes a power control means ( 12 ) for controlling the energisation of the receiver, a circuit ( 48 ) for detecting the presence of a carrier, which circuit ( 48 ) causes the power control means to de-energise the receiver ( 34 ) in the event of carrier not being detected, and a signal quality measuring stage ( 50 ) for determining if the demodulated signal is decodable, the stage ( 50 ) causing the power control means to de-energise the receiver ( 34 ) in the event of the signal quality not being acceptable.