Smoke and CO alarm planner
Count your levels, bedrooms and sleeping areas. We estimate the smoke and carbon monoxide alarms an inspector will look for.
Typical starting point
- Smoke alarms: at least 2 (one on every level and one outside each sleeping area). Newer-home rules and NFPA 72 also put one inside each bedroom: about 5.
- CO alarms: at least 2 (one on every level and near each sleeping area).
- Massachusetts: older homes may use battery alarms, but replacements often must be 10-year sealed units, photoelectric near kitchens and baths; the local fire department applies 527 CMR and your home’s build date.
This is a planning estimate, not an inspection. Your town’s fire department decides what passes, based on when the home was built or renovated.
How inspectors count alarms
Most resale inspections check that there is a working smoke alarm on every level of the home, including the basement, and outside each sleeping area. Homes built or renovated under newer codes need alarms inside every bedroom too, often interconnected or hardwired. Carbon monoxide alarms are required when the home has fuel-burning equipment or an attached garage.
Requirements depend on when the home was built and on state rules, so the fire department that issues your certificate has the final word. Look up your town’s fee and application on our state pages, and read how to pass the first time.