Measure / monitor ambient CO levels in home and office spaces. Visual and audible alarm indicates unsafe CO levels.The 770 is a state of the art carbon monoxide instrument designed to measure CO in ambient air. This palm-sized unit displays readings in 1ppm increments. Measure CO from O to 999ppm Displays the max. CO reading in PPM since power on Displays in hours and minutes, time elapsed since power on Displays user set value of audible and visual alarm The audible alarm can be switched on and off by pressing the SEL buttonPlease see Technical Information below for more information on this product.