Abstract: Underwater signal apparatus includes a waterproof housing having two chambers, a sealed chamber in which is disposed a transducer and electrical circuitry associated with the transducer. In the second chamber is a battery for providing the necessary electrical power for the transducer and its circuitry. The battery compartment is accessible for changing the battery. The transducer comprises one wall of the sealed chamber and is thus in direct contact with the water. The transducer circuitry is activated by a magnet movable on the housing. Within the sealed chamber in the housing is a magnetic read switch which is closed by the proximity of the magnet movable on the exterior of the housing.