Reference

Smoke detectors last 10 years from their manufacture date — not the day you installed them — under NFPA 72, and CO alarms enforce their own end-of-life clock under UL 2034. This guide shows how to read the date code on the back of the alarm, decode low-battery vs end-of-life chirps by brand, and walks a full replacement example.

Carbon monoxide detectors do expire, because the electrochemical CO sensor inside has a finite life and degrades whether or not the alarm has ever sounded. UL 2034 governs these alarms and requires an end-of-life warning. This guide covers sensor lifespan, the date code on the back, the end-of-life chirp, and a worked replacement example.