Product Reviews

Verdict: 4.0/5. The First Alert CO400 is the most affordable CO alarm in First Alert's lineup — 9V battery-powered, 85 dB, UL 2034. No display, no interconnect. Best for supplemental protection and smaller spaces. 5-year warranty.

Verdict: 4.0/5. The Kidde KN-COB-LP2 is a compact battery CO alarm with no display — reliable UL 2034 protection at budget pricing. Best for secondary placements, RVs, and emergency kits. Step up to KN-COB-B-LP for a display.