The device is used for detecting the presence of a liquid within a pipe or container, especially for the secondary protection of submersible pumps. It is connected to electrodes. It is installed in an electrical panel on a standard relay socket. The operating principle of the device is based on the measurement of the difference in the resistance between the electrode and the ground. It checks for the presence of water and maintains the relay activated if water is detected, or releases the relay if no water is detected. The use of safe, low AC voltage between electrode and ground prevents the phenomenon of electrolysis.