A drop detection part that detects drop into the water, a light emission part, and a light-emission control circuit that makes the light emission part emit light when the drop detection part detects the drop into the water. Also, the light emission part may be disposed on the side to be turned up by buoyancy when the device is dropped into the water and the drop detection part may be disposed on the side to be turned down in the case of the drop into the water, for example.