With less than $50 of off-the-shelf hardware and a little bit of programming, it’s possible for a hacker to gain instant, untraceable access to millions of key card-protected hotel rooms.
SJS-ONE is an open source 8-bit mono synthesizer from Devsound in Sweden that uses an Arduino as it’s brains. Looks to be nicely hackable (i.e. within the reach of the less geeky).