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.

CO alarm laws are a state-by-state patchwork: some states cover every home, others trigger only at new construction, sale, or rental, and coverage often hinges on fuel appliances or an attached garage. This guide maps the NCSL compilation into one table, explains UL 2034 and IRC R315, and walks a sale-state compliance 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.