Klein Tools has been making professional-grade hand tools since 1857. The ET110 isn’t a typical home alarm. It’s a meter designed for HVAC technicians who need precise carbon monoxide readings, not just a warning when levels get dangerous.

The display shows CO concentration in parts per million alongside temperature in Fahrenheit or Celsius. That dual readout matters when you’re diagnosing a furnace or verifying a repair. The backlit screen is readable in dim basements and crawl spaces. An audible alarm and flashing red light trigger when CO hits unsafe levels. The unit runs on four AAA batteries and includes a carrying pouch. It feels solid in hand, with a rubberized grip that won’t slip.

One honest limitation: this is a diagnostic tool, not a 24/7 safety monitor. It won’t sit on your nightstand and alert you while you sleep. For professionals or serious DIYers who need to measure and log CO levels, it’s precise and straightforward. For basic home protection, you’d want a dedicated plug-in alarm instead.