Klein Tools ET110 Carbon Monoxide Meter - 0 to 1000 ppm, Low/High/STEL Alarms

Carbon monoxide is the diagnosis an HVAC tech can't make by feel - it's colorless, odorless, and the difference between 30 ppm and 300 ppm is the difference between a note on the invoice and an evacuation. The Klein ET110 puts the number on a backlit LCD: CO concentration from 0 to 1000 ppm at 1 ppm resolution, with a replaceable electrochemical sensor rated for a 5-year life and a T90 response under 60 seconds. Accuracy runs +/-5% (or 5 ppm) in the 59-77°F midrange, and MAX/AVG functions cycle through maximum, minimum, and average readings for documenting a call. Ambient temperature displays in Fahrenheit or Celsius.

The alarm structure does the safety thinking with you. A low-level alarm trips at 35 ppm (the NIOSH 8-hour recommended exposure limit) and a high-level alarm at 200 ppm, both audible and visual with a warning indicator light - and the short-term exposure limit (STEL) alarm (200 ppm over 15 minutes) adds protection against the accumulating doses a simple threshold misses. Auto power-off after 20 minutes of inactivity conserves the four included AAA batteries.

Two honest cautions: this meter is not intended for use as personal protective equipment, and it is not insulated. It's a diagnostic instrument for finding, measuring, and documenting CO conditions at furnaces, flues, boiler rooms, and gas appliances - not a substitute for a personal monitor in confined-space work. For HVAC pros, inspectors, and property techs, it's the fast answer to "is this appliance making CO, and how much." Carrying pouch and batteries included; 3.3 ft drop protection.