Happens all the time. Seen it with phones and radios alike. The door entry
card my company uses sets off Walgreen Pharmacy, Burlington Coat Factory,
and Macy's almost 100% of the time. Its doesn't happen in other stores. I
assume its related to the brand and model of loss prevention systems they
use. Most of these systems use a concept called "RF tags", where a small
resonant circuit inside the inventory control tag resonates and responds
with the "right" code and sets off the alarm. Its powered by induction, or
the electromagnetic field generated by the sensors near the door. Sort of an
advanced version of moving a coil around a magnet to generate a current.

Door entry cards of this type (not to be confused with ones you have to
"swipe" like a credit card) use a technology similar to RF tags, but a bit
more complex. It allows the card to be read simply by being near the touch
plate. I've concluded that it sets off store systems because the card's
circuit is activated by the store's inventory control sensors and the system
is too dumb to tell the difference between my card and a inventory tag. To
avoid setting these off, I just try and remember to leve my id at home or in
the car, or if I forget, I hold it over my head as a I walk in (though I
admit that does attract some funny "looks").


"nana" wrote in message
...

Lets not forget, an amateur license carries a higher degree of respect
than does a non licensed device.


With whom? Most people still have no accurate idea what a Ham is!

In regards to this ancient thread - my cellphone has triggered the alarms
at the checkouts more than once. These alarms relied on reradiation of
harmonics and perhaps some non-linear device within the phone did just
that.

The store did not go into an anti-theft frenzy. The girl looked up from
her register, I took my phone off my belt, waved it past the detector, it
beeped, I walked through after it, it didn't beep, problem solved. There
is no big issue here.

Brad VK2QQ