With the CO15, checking CO levels is as easy as pushing just 1 button on the model CO15, which measures up to 999ppm. An audible alarm indicator will continuously beep starting at 25ppm (preset warning level - value can be adjusted) and the display will flash until the CO level goes down to normal range. A backlight on the display can be used for low light areas. The meter comes complete with batteries, wrist strap, and pouch.