Anti theft gate things in shops/libraries.

[Disconnected]

Aight, so I've been going into/out of the library a lot lately to study since my desk at my flat sucks. I usually listen to music on headphone when walking to/studying in the library, and I have noticed that when I walk through the little security gate things (the two panels on either side of the exit that beep if you have an item you shouldn't) my earphones my a high-pitched ring.

I am assuming there is an induced current in the wire of the headphones from my moving them through some field, which made me realize I have no idea how the gate things work.

So, it got my curiosity going, and I figured I'd see if anyone here knew and could explain it to me in understandable terms.

So, yeah. How do they work? Why are my earphones ringing?

Thanks dudebrohamskis.

 

[fss]

It's a low-frequency RFID system.

http://electronics.howstuffworks.com/gadgets/high-tech-gadgets/rfid.htm

 

[Disconnected]

Thanks man! That article is interesting. Cunning stuff.

I also got a good chuckle out of the lady warning everybody that the tags could be "the real life mark of the beast".

 

[Jiggy-Ninja]

It's a low-frequency RFID system.

http://electronics.howstuffworks.com/gadgets/high-tech-gadgets/rfid.htm

Audible frequency radio waves? Wouldn't the antennas have to be gigantic for that?

So those little white plastic tags they stick on some things that are impossible to peel off are RFIDs?

 

[berkeman]

Audible frequency radio waves? Wouldn't the antennas have to be gigantic for that?

So those little white plastic tags they stick on some things that are impossible to peel off are RFIDs?

The RF causes interference with the audio circuits in the music player. Kind of like a form of demodulation...

BTW, funny (now) story -- I bought a new wallet one time, and when they blasted it at checkout to blow the diode in the RFID circuit, it turned out that it didn't blow. So every time I walked in and out of a Target store at the mall, I'd set off the beeper things. Very annoying. I looked all through the wallet, and could not find anything, and then finally got desparate one day and practically tore it apart. Finally found the super-thin RFID antenna and circuit. Whew!

 

[fss]

Audible frequency radio waves? Wouldn't the antennas have to be gigantic for that?

Not necessarily.

So those little white plastic tags they stick on some things that are impossible to peel off are RFIDs?

Usually.