🚀 go-pugleaf

Hi folks:

I was wondering how in the world the anti-theft systems
work in shops. They look as follows:
At the exit, there are two parallel boards, standing up.
A person leaving the shop/library always has to pass *between*
these boards. The boards are attached to electronic stuff.
Articles bought in the shop are for example (in case of books)
'rubbed' over a plate. In case this hasn't been done properly,
or NOT at all (theft !), the alarm goes off when passing through
the gate.
When not concerning a shop selling books but other articles, like
CD's, the same anit-theft system is installed. People suggested to me
that in that case, something is attached to the article under the price-label.

How in God's name can this work ??
Electrical Field ? Magnetic Field ?
Space-vibes ?

If one of the first two is used, shouldn't it be a very strong field,
for such a great distance between the boards ?
And how about deviations by human-tissue, a watch, a belt etc. etc.

Could someone enlighten me ? I am feeling stupid here ...

Send for instance an Email. In case of THE answer, I'll post it ..
My mail-adres is : kolks@imec.be

Thanks


Tilman Kolks at:
	Imec,
	Kapeldreef 75,
	B-3001 , Leuven
	Belgium
	Email: kolks@imec.be