Yes.
They are and can only be a rough guide. My old Neon one when I could see
could light up if you just laid a wire alongside where a mains cable went. I
imagine the newer kind use some kind of fet and an led to do the same job,
but either way, I'd not want to trust on myself.
The only use I ever found for them was as a confidence check that an
appliance was absolutely dead and disconnected. Anything involving runs of
wire will be very ambiguous.
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"D.M. Procida" wrote in
message
...
I noticed that the wire into a ceiling lamp lit up an electrical
screwdriver when I checked its terminal, and it did the same at the
switch end - even when I completely disconnected it from both ends.

I'm pretty sure that this was a single uninterrupted wire from switch to
lamp, with nothing else connected to it, but I can't be 100% certain.

I assume that there was a very low induced current in the wire from some
other nearby wire; whatever it was, I couldn't actually feel anything
myself when I touched it.

Is this normal behaviour for an electrical screwdriver, to be so
sensitive?

Daniele