Quote:
I'll bet it was a digital meter right?

Old school electricians tend to use solenoid voltage testers like this one. These testers have low impedance which eliminate the "phantom voltages" caused by induction. Sure they are not precise to the sub-digit, but most of the time, they just want to detect if voltage is present or not and they do that job better than anything else.

The high impendace(resistance) of digital voltmeters is useful to prevent introducing errors in readings by limiting the "alternate path" of electrons through the instrument. Low resistance of the instrument would reduce the overall circuit resistance and thus reduce voltage. When testing home wiring, there's usually no need to bother with precision, so low impedance instruments is all right.


Concerning the "phantom voltage": Imagine the open wire as a current source instead of a conventional voltage source. It is able to supply no more than maybe 3 uA. When you close the circuit with a 10 megOhm instrument, this gives a 30V drop across that instrument. If you measure voltage on that wire with a solenoid voltage tester which have a 4 kOhm resistance, voltage would only be 0.012 V.

I hope I'm clear. It seems obvious in my mind using French. It's a bit more cloudy in English ;-)