A float switch is a device used to detect the level of liquid within a tank. The switch may be used in a pump, an indicator, an alarm for water level in the tank. We have float switches range from small to large. It is a mercury switch inside a hinged float. A series of optical or conductance sensors produce discrete outputs as the liquid reaches many different levels within the tank. A float switch is used with water level controller indicator to know the current water level status in the tank.