We all know about hardware keyloggers, but it seems to me that the concept of filtering keystrokes at the physical level gets even easier when people use wireless keyboards. To my knowledge, a wireless keyboard more or less just encodes ASCII characters, and then beams them to the little USB dongle via ~2.4GHz RF.
Isn't it technically possible to intercept these transmissions if you got close enough to someone [say, the next cubicle over?] with something like this and have essentiallty a wireless keylogger? Are these keyboard transmissions encrypted in any way? Is there any way to defend against this if they aren't?