The Best Carbon Monoxide Detectors
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Ryan V. Editor-in-Chief
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Most carbon monoxide alarms do one thing when they sense gas: they sound an 85 decibel horn. The Kidde Nighthawk KN-COPP-B-LPM does more. Its backlit screen shows the live reading in parts per million and refreshes every 15 seconds, so you can tell the difference between a brief cooking blip and a real climb. It also keeps a peak-level memory, storing the highest concentration it has seen since you last reset it, which matters because CO can spike and clear before you walk in the door. This Old House rated the Nighthawk line 4.7 out of 5 and named it Best Plug-In, and SafeWise praised how easily it installs. It runs on AA batteries, so there is no wiring and no outlet to find.
What It Won't Do
Kidde's own store lists a seven-year unit life and a five-year warranty for this model, shorter than the sealed ten-year alarms, and there is no app if you want alerts on your phone.
The Kidde KN-COB-B-LPM strips the alarm back to the job that saves lives and sells it for less than 35 dollars. It uses the same electrochemical sensing as Kidde's pricier units and meets the UL 2034 sensitivity standard, so it triggers at the concentrations that matter. It runs on three included AA batteries and mounts anywhere with no wiring, and it carries a ten-year life and ten-year warranty, actually longer than the Nighthawk above it. What you give up is the display: it sounds an alarm without showing the number.
What It Won't Do
There is no digital readout, so it warns you without telling you how high the level is, and Kidde now lists it as an earlier generation, so stock varies by retailer.
Who Should Buy Which
Kidde Nighthawk KN-COPP-B-LPM CO Alarm with Digital Display
The reference standalone CO alarm, with a live ppm readout and peak-level memory
- Anyone who wants to read the actual CO level, not just hear an alarm
- People who want peak-level memory to catch a spike that has cleared
- Renters who want a battery unit with nothing to wire
Kidde KN-COB-B-LPM Battery-Operated CO Alarm
The cheapest reliable way to get a UL 2034 CO alarm on every floor
- Anyone outfitting several floors for the least money
- Buyers who want a trusted UL 2034 alarm and no extras
- People who prefer a ten-year life with three AA batteries included