Brandon Dunson developed his own bathroom fan trigger based on stinky or humid air conditions. The initial inspiration for the project came from a twitter-connected fart sensing office chair. Hiding behind the character display you can see the MQ-4 methane gas sensor which he picked up for the project. But since thereâ€™s also a shower in the bathroom he included a humidity sensor with the project. Both are monitored by an ATmega328 which averages 10 readings from each sensor before comparing the data with a set threshold. If the sensors read above this level a relay turns on the bathroom fan.