TPI Carbon Monoxide Monitor: Pocket size, Displays readings from 0 to 999ppm, Records maximum CO readings in ppm since the unit was turned on, Alarm setting displays the value the alarm is set at (factory set at 30ppm). Alarm sounds when preset value is reached 1 Year warrenty: OUR TALK this unit should be the first thing you enter a property with, and the last thing you turn off when you leave, It could save your life.