Fluke ST120+ GFCI Socket Tester with Beeper - Fluke Corporation Just plug the socket tester in, walk to the circuit breaker panel, and listen for the beeper to turn off – or on – as you flip the breakers. Once it does, you’ve found the correct breaker. Time – and trips – saved. When switched on, the integrated beeper can also alert you to hazardous voltage at the outlet, even if the wiring is Fluke 1507 Insulation Resistance Tester | Fluke - Fluke Corporation Nov 02, 2021600 V AC rms or DC: Storage temperature-40°C to 60°C (-40°F to 140°F) Operating temperature-20°C to 55°C (-4°F to 131°F) Rated 5 out of 5 by Twinson from Great tool Great tester! We use it for testing wiring after flood or fire damage. Very useful tool. Easy to use and a larger display make this a great tester. Date published: 2016