I bought this plug in first alert cm detector. The Gas Co rep told me that it only detects at 70ppm, which means I'd likely already have headaches and be vomiting. He recommended I throw it out and buy a cm detector that detects at 400ppm. Also, he said socket plug ins are not effective as most sockets are low on the wall. The best kind is a battery operated detector (400ppm) that is placed within 2 ft of the ceiling. The idea is to be notified before you/family gets headaches and start vomiting.