My hackathon project came third at the Met Office Weather for Fun hackathon in Exeter on 6/7 October.
The idea was to build a very low weight (less than 10 gram) temperature sensor that could be carried by a toy helicopter. OK, not a very practical, or useful thing, but an interesting challenge. We did get it working using a Texas Instruments eZ430-RF2500 wireless micocontroller and TMP006 thermal infra-red sensor. The ground station used an eZ430-RF2500 and Arduino Uno.
Read about this and the other projects on Storify http://storify.com/hackdayhack/weather-for-fun-hackathon