Uxcell Stainless Steel Dual Ball Liquid Level Sensor Vertical Float Switch 6.69 A float switch is a device used to sense the level of liquid within a tank. The switch may actuate a pump an indicator an alarm or other device. It can be easily converted from normally open to normally close by inverting the float. Note: because the current that the switch can carry is much little(0.5A) you must use a relay or contactor when it is connected by a load relay or contactor are not included here.