The Extech carbon monoxide meter measures CO levels from 0 to 1000ppm. * Range: 01000ppm. * Easy-to-read 1999 count backlit display. * Pocket-sized, ergonomic body. * Simple one-button operation. * Audible alarm alerts user when levels exceed 35ppm. * Max Hold button captures peak reading. * Data Hold button holds reading in display. * Auto power off prolongs battery life. * Includes 9V battery, protective rubber holster and carrying case.