The tester worked fine a couple of times, but then it broke and there is no way to check it. I also had a pen in my mouth so I could use the flashlight while I was working. And I've dropped it a few times which must have broken it BUT it still comes on, the light still works. It just doesn't tell you if current is present under voltage. So you think it works, but it doesn't warn you when the cable is live. An easy way to think the power is off when it's still on.