Summary A motion transducer adaptable to radio telemetry has been designed and described. The transducer was evaluated by studying activity of the infant, sheep, cow and pigeon. Evidence of the motion transducer' versatility is presented by typical recordings from 4 subjects. Activity recorded included walking, trotting, eating, flying and respiration. Observation of the subject and record during initial recording periods permitted interpretation of records from unobserved subjects. Thus, the device was adaptable to monitoring subject activity over prolonged periods without constant observation.