When the robots rise up and try to overthrow human civilisation, you're going to want to be holding one of these. The Rfiddler gun fires an electromagnetic pulse that's designed to overload RFID tags.
It was built by Codeninja from a Nerf N-Strike Recon CS-6 with a 0.6 kilojoule camera flash driving a 50-turn copper spool. For added effect, the flash is still operational and an MP3 player has been hooked up to a 2-watt amp and speaker to make explodey noises when you fire it.
It should also be strong enough to take out a USB drive, too, and we wouldn't point it at anything else electrical that you don't want to lose either. It cost about 50 euros to build, including paint.