NASA is developing an electronic nose sensor that can detect concentrations of ammonia as low as 1 part per million (PPM). The human nose can't detect ammonia until it reaches about 50 PPM, although concentrations of just a few PPM can be dangerous to humans. NASA is concerned about this because the cooling system aboard the International Space Station is based on a complex network of pipes carrying ammonia throughout the station. The ENose sensor can identify other compounds as well and will probably become part of a complete atmospere safety system aboard the ISS. Meanwhile, medical and robotics researchers are looking into applications for the ENose here on Earth. For more, see the NASA Electronic Nose Project page or the recent press release on the ENose.