Abstract: A device designed to float in a home pool and sound an alarm when the water is disturbed, which is peculiarly sensitive to disturbances in the water, including a transducer for sensing noise in the water, a high frequency filter connected to the transducer, a saturable amplifier connected to the filter, an integrator connected to the amplifier, and a trigger circuit connected to the integrator for initiating an alarm. The integrator has a rise time on the order of fifty milliseconds so that it rejects moderately loud disturbances unless they repeat many times within a short period of time, as is the case in noise reflected off the walls of an average size pool. The decay time of the integrator exceeds five hundred milliseconds so that the integrator output builds up over the period of at least two or three major noise pulses of a typical moderate splash in water.