General Technologies Corp GTC CT8007 Cordless Polarity Computer-Safe Circuit Tester No Ground or clip required which means no wire tangles nor time lost searching for grounding points High Impedance electronic circuitry with negligible current draw ( 1 microampere) is 30,000 times less than regular lamp type testers allowing for complete safety when working around sensitive electronic control modules and sensors Operating range between 6 and 28 volt DC in battery powered systems Liquid crystal display indicates "CIRCUIT OK +" on contacting positive voltages, and "CIRCUIT OK -" on contacting negative voltages Lightweight high strength plastic construction with cap and clip and uses no batteries and maintenance free