"Lou" wrote in
erio.net:

Be it while receiving or transmitting or
carrying items such as pocket knives, etc. Maybe some alarms are more
sensitive than others, but I've not run into any - yet. Then on the
other hand, I've seen one go off even though a person in front of me
was checked out and tried to leave. They were checked and found all to
be in order, and told to go ahead. So, who knows?

Those anti-theft tag systems use a large antenna to detect the tags. The
field needs to be tuned, and whenever a pedastel or antenna gets moved,
the whole field can get out of whack. This is sometimes the reason for the
false alarms. I know I've had a fire radio set off one in a drug store once
out of the 1000's of times I've walked into a building with that radio.
Also, sometimes on high theft items, tags are hidden multiple times on
devices. Often times they cannot be de-activated, rather just makes sure
someones checking your receipt on your way out the door.
I've also had a tag stuck to the color of my shirt once, by a prank playing
co-worker. Had no clue, but everyone who passed through the doorways the
same time I did, nearly got a body cavity search

john