DROK Handy LED Digital Voltmeter DC 0-33V 12V/24V Voltage Meter Gauge Tester 4 Digits 3 Wires Volt Detector Power Monitor with Red Digital Display for Vehicle Auto Automotive Battery Monitoring Handy size(612918mm), 3wire simple installation, convenient and easy to install. 3-wire installation provides stable power supply,high brightness uniformity of digital tube. With reverse polarity protection to avoid burning and it will display "0" when over-range. Comes with two regulator chips, stable operation; wide input voltage: 7-30V. Great for monitoring automobile,car battery,motorcycle;allows you to grasp the battery power timely.