Klein Tools Non-Contact Voltage Tester detects standard voltage in cables, cords, circuit breakers, lighting fixtures, switches, non tamper-resistant outlets and wires. A bright green LED indicates the tester is powered on. It changes to red and an audible tone sounds when voltage is detected.WARNING Read, understand, and follow all warnings, cautions, safety information, and instructions in this manual before operating or servicing this tester. Failure to follow instructions could result in death or serious injury. Never assume neutral or ground wires are de-energized. Neutrals in multi-wire branch circuits may be energized when disconnected and must be retested before handling.