Home Smoke Sensors by Rooms

Residential smoke detector sizing

Both NFPA 72 (United States) and ABNT NBR 17240 (Brazil) ask for at least one smoke alarm inside every sleeping room, one in the hallway that serves those rooms, and one on every floor including the basement. Near the stove, but not right above it, put a kitchen-rated detector (photoelectric or heat) so normal cooking doesn't keep tripping it. The estimator leans conservative and works from detectors = rooms + 1 (hallway) + 1 (kitchen).

A standalone alarm has to hit at least 85 dB at 3 m. Test it monthly with the test button and swap the battery every year, unless you went with a 10-year sealed lithium model. Either way the whole unit gets replaced after 10 years, since the sensing chamber degrades. NR 23 (the Brazilian fire-protection rule) and the local fire brigade (Corpo de Bombeiros) cover non-residential buildings; for condos with common areas, NBR 17240 is mandatory.

Applications

Spec out a starter pack for a new home, or bring an older property up to today's life-safety baseline. Plan a set of interconnected wireless detectors so one alarm sets off all of them, and budget for the 10-year replacement cycle that comes around eventually.

FAQ

Where should I mount the detector? On the ceiling, kept at least 10 cm off any wall, and clear of supply-air vents, ceiling fans and bathrooms, where steam will set off false alarms. If the ceiling is pitched, mount it within 90 cm of the highest point.

Photoelectric or ionization? Photoelectric picks up smoldering fires (sofas, mattresses) sooner and nags you less during cooking. Ionization is quicker on open flames. Dual-sensor units handle both. Most modern residential models are photoelectric-only these days, mostly because they hold up better in real homes.

Do they need to be interconnected? It's strongly recommended. When detectors are interconnected (wired or over a wireless mesh), every alarm in the house goes off at once. That's what wakes someone sleeping at the far end of the house when a fire starts in the kitchen.