Patented Automatic self-test verifies the integrity of the unit. Bright LEDs and audible alarm sound if voltage is present. Silent-mode feature for use in quiet settings. Safe, non-contact voltage detection. Use to detect voltage in outlets, lighting fixtures, circuit breakers, wires and cables or to find a break in a wire. Automatically turns off after five minutes of non-use to conserve battery life. Low battery indicator. (2) 1.5 V AAA batteries included. Lifetime limited warranty.