The Kidde KN-COPP-B-LPM has battery backup for constant protection from the dangers of carbon monoxide poisoning even during power outages. With digital display levels are easy to read. Green and red LED lights advise of normal or dangerous CO levels respectively. Detects and stores carbon monoxide levels as low as 11 ppm and has a peak level memory feature. Sliding door allows access to batteries and will not close when compartment is empty. Also has a test/reset button to make sure horn and electronic circuitry are still working properly.