When I walk through the security gate at some retail stores, my keys tend to set off the alarm. After doing some research, the only explanation I could come up with is that a key or some part of my key ring might match the permeability of an un-scanned security tag. As I am physics-clueless, can anyone verify permeability as the most likely cause or suggest another reason?
Thanks in advance…
I don’t have an answer, but how can you be certain that the cause is your keys?
I wouldn’t think so. Maybe more can be discovered here
I once carried a small lenten cross made of Aluminium in my wallet, and it set off quite a few door security alarms (it now resides in my glove compartment).
It was small and thin, lightweight, about half the size of my (very manly) thumb, but it did the trick in setting off alarms in many (not all) places, even buried in my leather wallet (yes, it did take a while to realize that this cross was the cluprit).
Do you have any such metal items on you besides your keys, that perhaps you forgot about?
Well, regardless of whether it’s your keys or not, permeability is not the cause. Permeability is a layer’s ability to allow mass to flow through it, lungs, for exampe, are permeable to lots of gasses, most notable O2 and CO2. What I think you’re thinking of is most likely induction, though also possibly resonace. The security gates, as far as I know, use magnetic fields. When it changes to the alarm field, as set forth by those tag things, it goes off. Without going into a lot of physics here, inductors…well…induct. That is to say, they make there own field in the presense of another, thus changing the overall field. I think. Someone will come along and correct me if I’m wrong…but I do know that it’s NOT the permeability of your keys…which I hope is zero.
There are two types of merchandise security devices.
The little white plastic one have a thin flat piece of magnetic metal, pointed at both ends and adhered to one side of double sided tape.
There are also two rectangular pieces of the same material curved along their length. Now usually inside and hard to get at to remove.
The second one is an very adhesive sticker, sometimes inside or outside disguised as a price and bar code sticker. This has a printed circuit or two of conductive ink and a center containing a switching circuit to activate/deactivate.
Both appeat to be magneticaly activated/deactivated and sensed at the store entrance by electromagnetic radiation (R.F.)
“Bewar of the Cog”
Amorphous metals for shoplifting detection.
If that’s the problem, you might eliminate it by either tossing your keys in a pot of boiling water for a few minutes, or running a strong magnet over them.