The Testo 317-3 Ambient CO Stick detects carbon monoxide in ambient air and warns the user visually and audibly of dangerous CO concentrations. It is ideal for furnace and boiler service, weatherization audits, and home inspections.

Key features include a 0-1,999 ppm CO range with 1 ppm resolution and ±5% accuracy. No zeroing is required, and the adjustable alarm threshold allows users to set the alarm at safe limits. A self-test mode verifies CO sensor function without test gas. The CO cell carries a 3-year warranty.