Abstract: An alarm arrangement for swimming pools includes an electronic transmitter unit (16) and an electronic receiver unit (18). The transmitter unit (16) has a housing (20) containing electronic circuitry. Water activated electrical contacts (24, 26) are provided outside the housing (20) for causing energization of the electronic circuitry when coming into contact with water for emitting an ultrasonic operative signal when a person wearing the transmitter unit (16) enters into water in a pool. The receiver unit (18) has a housing (36) containing electronic circuitry, water activated electrical contact (54, 56) outside its housing (36) for causing energization of the electronic circuitry when coming into contact with water, for detecting any preselected operative signal from the transmitter unit (16) when the transmitter unit (16) comes into contact with water in a pool so as to emit a suitable alarm signal.