The Medway Handyman formulated on Wednesday :
I have a non contact 'voltstick' which is used as you describe. Always
wondered though, why does it light up if waved rapidly from side to side? No
idea how they work.

They detect the field around the cable. Your waving it about moves it
through a field, which is a good before and after check of the volt
stick.

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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk