Pocket CO Model 300 is the world’s smallest and most affordable carbon monoxide detector, alarm and dosimeter. About the size of a key fob and weighing less than 1 oz., this wearable instrument is a highly sensitive, reliable and popular instrument. Range: 0 – 500ppm; first alarm at 50ppm, second at 125ppm, third at 400ppm. Also has an 8-hour TWA warning alarm at 25ppm. The instrument self-checks upon start and carries a 2 year instrument warranty.