Features: The two wires are used regularly. The red connected- to the positive, the black connected- to the negative, and the reverse connection protected. Normally, no external working power-supply needed, and the measuring voltage can be directly operated. The measuring voltage range: 5V-19.9V. Bright LED display, and it well made, the strong plastic cases prevents it from easily damaged by outer force. Operating voltage: no need to connect to any power-supply, two-wire systems. Suitable for most vehicles, such as automobiles, ships, substation-automation, distribution-automation, test equipment. its practicability enough to meet your various-need. Package Includes: 1x Digital Voltmeter Specifications: Material:ABS Detection Voltage:5V-19.9V LED Color: Red/ Green / Blue Size:Approx.5.6x2.9cm/2.2''x1.14'' Cable Length:Approx.70cm/27.56'' note: Please allow 1mm errors due to manual measurement. Due to the difference between different monitors, the picture may not reflect the actual color of the item.