GTR Technologies Dewstop Condensation Detector
Condensation can turn a bathroom into a mold factory that ruins tile and triggers allergies. DewStop's weather-prediction software turns on the bathroom fan when temperature and humidity levels get too high, and it predicts how long the fan should run based on how much water vapor is in the air, so the fan won't waste energy or shut off too quickly. And whereas other detectors require installing a new ventilation system, DewStop easily connects to existing bathroom fans.
Unfortunately, this device doesn't detect odors. The better high tech solution is a motion sensor like is used for lighting. It will turn on the fan when someone enters the room and then time itself off after they leave.