Abstract: A switching device for effecting electrical continuity in an alarm circuit in response to the wave motion created by the ingress of a relatively large object into a pool of water or the like. The device includes an elongated member having an open interior chamber adjacent to its upper end, said chamber communicating with the exterior of said device and containing a float which is longitudinally movable within the chamber to effect electrical continuity between a pair of spaced electrical terminals in the member. The device is floatable in a pool of water or the like with at least the top portion of said member and said chamber above the surface of the water and with the bottom portion of said member extending well beneath the surface of the water. As the member bobs or oscillates in the water, the float moves upwardly within the chamber to effect continuity.