To answer the original question:
Would anybody trust a non-contact voltage tester? (such at the Fluke 1AC-A1, the pen shaped testers that glow in the presence of voltage and fit in your pocket) Would you trust it enough to touch a bare wire or terminal strip that nomally has 600 vac. on it if the "volt pen" showed no presence of voltage?
In a nutshell, no I wouldn't.
Batteries can go flat at any
I'd only touch a wire that was shown to be dead by a non-contact tester, after having re-tested it with a reliable contact type tester.
Non-contact testers use a Hall-effect sensor in the tip to detect the changing magnetic field from the AC voltage in the wire, the batteries are used to drive either an LED indicator or a small piezo unit or in some cases both.
Having had experience with non-contact testers up to 66kV level, the importance of having good, well looked after test gear and the need to constantly check the testers integrity, really sinks in.
To have a tester fail at these kinds of voltages, would be devastating.