Abstract: A diaphragm switch having a lower contact on the upper, interior, surface of a flexible membrane is pressed upward against an upper contact when the membrane is displaced upward by a rising water level. Closing of this diaphragm switch completes an electrical circuit including a power source, an annunciator, and wiring causing an alarm to be sounded indicating that a certain water level has been attained. The alarm may be silenced with release of an on/off switch or the alarm, attached by suction to an interior surface of a bathtub wall, may be displaced upward or removed. Catching the on/off switch sets the alarm and a visual indicator light may indicate this state. The top surface of the alarm may be a platform for a soap bar. The entire alarm is waterproof. Different standard sized batteries and appropriate enclosures permitting replacement are suggested.