Hotel key card

[resabed01]

My curiosity on how things work had me peeling the layers off this hotel key card. It's not the usual magnetic swipe card but rather a proximity card that you wave in front of the door lock. I found inside what appears to be silver traces printed on the substrate. I peeled away an area on the left side of the card months ago and now it looks oxidized and tarnished, much like silver would behave. I don't have any nitric acid here to test.

I imagine other proximity cards would have a similar antenna built in.

I still don't know how the card works, i can't find a chip.

 

[pimpneightez]

Ive only seen proximty cards with a copper coil antena. They usually have a small capacitor and Intergrated circuit as well. They use radio frequency fields. The one you have looks like it has a smaller range. I would say you need to be within 4" of the lock for it to work.