[Tim] noticed a 2.4Ghz WiFi spectrum analyzer on thinkgeek a while ago and got curious. He knew that the spectrum analyzers with which he was familiar were giant expensive units, so he got curious what this little dongle was. It turns out, it really wasn’t much at all. Just a simple wireless receiver. He decided that rather than spending the $399 for one, he would toss one together using an Xbee. His total cost ended up at roughly $50 for basically the same unit. While he doesn’t give a schematic, you can download his source code on the site.
Hack
WiFi spectrum analyzer
Hack
Build a wireless keylogger
Hardware Keylogger solutions has released the plans and files for their wireless logger. It has a range of about 50 yard between the transmitting dongle and the receiver. It is based around an Atmel AT91SAM7S64 and the PCB is pretty tiny. In case you hadn’t noticed yet, they sell them as well. The cool thing about this is that key data is transmitted in real time, allowing you to see it as it happens instead of having to go retreive the log physically like you used to.