The HYDROS Water Level Sensor contains no moving parts that can fail. Its extremely tiny: its a little over a half-inch thick with a circumference the size of a US penny. The optical eye is magnetically coupled with the magnet side measuring only thick. It can be mounted to most clear, tinted, or painted surfaces up to thick. The sensor operates in the daytime or complete darkness so its safe for use hidden inside your aquarium stand or in the back chambers of an all-in-one aquarium. The sensor is easy to place, easy to move, and easy to clean. The sensor connects with any HYDROS Sense Port using an aviation-style plug for safe operation. No additional power source is needed to run the sensor.