A float switch is a device used to sense the level of liquid within a tank. This switch may actuate a pump, an indicator, an alarm or other device: because the current that the switch can carry is just 500mA, you must use a relay or contactor(not included). It can be easily converted from normally open to normally close by inverting the float.
This type of sensor is often used in mechanical equipment, such as environmental protection air conditioning, water cooling fan, water heater, water dispenser, dishwasher, etc.