this is an auto top off ( A.T.O.) and water level too high alarm. i used a juction box from lowes to house the items, there is a 12v power supply that connects to a relay so there is only 12v to trigger the A.T.O. float switches, this keeps the 120v away from the water and hopefully save the float switches from burning out. the alarm is wired to 3 "AA" batteries so if the power goes out the alarm will still work, i was going to install a LED to test the batteries by pushing a button on the faceplate but.. i ran out of room inside the box! enjoy