Reference

Modern UL 217 added three tests no residential smoke alarm had to pass before: smouldering and flaming polyurethane foam fires, and a cooking nuisance test the alarm passes by staying silent. This guide covers how the 8th, 9th and 10th Editions differ, what NIST measured on real alarms, and whether yours must be replaced.

Two hardwired smoke alarms can share a connector and still be incompatible, because interconnect compatibility is defined by published model lists rather than by whether the plug fits. This guide reproduces the Kidde, Firex, First Alert and BRK model lists, the adapter that bridges some pairs, and the device and wire limits.

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.