Smoke Detector Basics

Everyone knows that smoke detectors save lives, and most people know you’re supposed to test them regularly and change the batteries every so often, but there’s more to smoke detector safety than just these items.  Smoke detectors should be located throughout the home, properly installed, and replaced every so often.

Locations: The Minnesota State Building Code requires smoke detectors in every bedroom, in the hallways outside the bedrooms, and at least one on every level of the home.  I’d guess that about 50% of the homes that I do Truth-in-Housing Evaluations on in Minneapolis and Saint Paul have working smoke detectors on each level, and maybe 10% have working smoke detectors in each bedroom.  There is a lot of room for improvement in these cities.

Installation: Smoke detectors need to be installed in accordance with the manufacturer’s recommendations to operate properly.   This typically means that if a smoke detector is installed on the ceiling, it should be at least 4” away from any wall.  If a smoke detector is installed on a wall, it should be 4” to 12” down from the ceiling - no more, no less.  The diagram at the right helps illustrate this.  This is required so the smoke will reach the detector and set it off in a timely manner.  How important is this?  Watch the video below to get an idea.  The best place to put a smoke detector is on the ceiling in the middle of the room.

Replacement: Smoke detectors should be replaced according to the manufacturer’s requirements.  Typically, this is about once every 10 years.  You can usually find the replacement date on the back of your smoke detector.  The photo below is from the back of a smoke detector which was manufactured in 2007.


Testing: Test the smoke detector using the built-in test button.  This is the preferred method, and will accurately test the unit’s operation as required by Underwriter Laboratories.  Again, follow manufacturer’s requirements for how often to test – the smoke detectors I have in my house are supposed to be tested weekly.
Batteries: Smoke detector batteries should last at least a year.  There’s nothing wrong with replacing the batteries annually, but you can also wait until the low battery indicator starts going off – this usually consists of an annoying chirp every 30–60 seconds.


Hardwired Detectors: Unless you live in Saint Paul, this isn’t required in older buildings.  Saint Paul requires at least one hardwired smoke detector near the sleeping areas on all existing homes, even on old homes that didn’t require this at the time of construction.  For the rest of Minnesota, if remodeling occurs, smoke detectors need to be hardwired and interconnected if there is access to wiring.  If there is no access to the wiring, battery operated smoke detectors are acceptable.

The following link has more specific information on Minnesota Smoke Detector Requirements.


Reuben Saltzman, Structure Tech Home Inspections - Email - Minneapolis Home Inspections