An awesome, albeit frightening device from Samy Kamkar – for around $10 you can be the proud owner of the KeySweeper, an Arduino-based sniffer/decrypter/keylogger that targets Microsoft Wireless Keyboards.
It conveniently masquerades as a USB charger, so it is reasonably small and completely discreet. I am not sure about where you work but these devices have been omnipresent at most workplaces I’ve encountered, quite often (and not surprisingly) attached to Apple devices.
All keystrokes are logged online and locally. SMS alerts are sent upon trigger words, usernames or URLs, exposing passwords. If unplugged, KeySweeper continues to operate using its internal battery and auto-recharges upon repowering. A web based tool allows live keystroke monitoring.