London Hackspace has an RFID card entry system that lets people register whatever RFID card they have in order to unlock the door (Since we're in London, most people are using Oyster cards).

Since I got a Galaxy Nexus I've been interested in playing about with it's NFC support, which is a layer on top of the usual RFID stuff.

I've written an Android App that uses your phone to grab the serial from an RFID card and then add it to your Hackspace account. So if you've got a phone that supports NFC you can add your own card your self.

apk here:

http://pointless.net/~jasper/LHSSelfEnrole.apk

and code here:

http://pointless.net/hg/lhsselfenrole/

to use it:

• install the apk.
• run the App.
• wave card at back of phone, observe serial number appear in 'serial' field.
• enter LHS membership Username and Password in the supplied fields.
• hit 'Go!'
• relax and let technology do the rest for you...

I was hoping to be able to generate a random serial number and get the phone to pretend to be a card and use that to activate Doorbot, but I haven't worked out how to yet. (The android SDK really focuses on NFC stuff, not the lower level RFID things, so it might be a bit like trying to spoof a mac address from http).