Quickly check the operation of DC proximity sensors or level switches without dismounting. Designed to test any three or four wire sensor with a solid state switch output. The A-800 provides visual and audible indication of whether the switch is operational. Switch status NPN/PNP indication is designated by a yellow LED. Power "on" is indicated by a bright green LED. "Low Battery" is indicated by a red LED. Unit can be used with capacitive, inductive, or photo electric sensors. The pocket sized A-800 is supplied with a two 9 volt battery.