Smoke Detector Locations and Why They Beep at 2:00 AM

smoke detector

The most common question I get asked is if it is required a house be brought up to current safety standards at the time of sale.  The answer, as I posted here, is generally no, except for a few items..

California requires smoke detectors and carbon monoxide detectors be installed in specific locations at the time of sale.

The specific locations are found in Cal. Health and Safety Code section 13113.7


A smoke detector is required in every bedroom. No exceptions

A smoke detector is also required outside each area of the bedrooms. Meaning if you have several bedrooms located together with a hallway in common, a single smoke detector in the hallway is ok. But if the bedrooms are in different areas of the home, then you need a smoke detector outside of each area of the bedrooms. A carbon monoxide detector is also required outside each area of the bedrooms. A smoke and carbon monoxide combination detector is legal.

One per floor

There should also be at least one smoke detector and one carbon monoxide detector per floor, regardless of if the floor contains bedrooms or not.

carbon monoxide detector
carbon monoxide detector

Common Misconceptions

I read reports from other home inspectors all the time that recommend smoke detectors in other rooms. And while more smoke detectors may be better than fewer, there is simply is no requirement that a detector be placed in a garage, laundry room or kitchen.

I do suggest an additional carbon monoxide detector be placed near any gas water heaters or gas furnaces if they are located inside the living space that is not near an existing required location, but that is only a recommendation and not a requirement.

smoke and carbon monoxide detector combo
smoke and carbon monoxide detector combo

Why Do Smoke Detectors Beep at 2:00 AM?

We have all experienced a smoke detector chirping, and almost always at the most inconvenient time, like 2 am. So why is it always around 2 am? Murphy’s Law? Coincidence? A conspiracy to prevent you from getting a good night’s sleep? No, actually the answer was uncovered by my friend Philippe Heller, President of The Real Estate Inspection Co in San Diego.

Smoke detectors are designed to chirp when their batteries are low to warn you it’s time to change their batteries. Batteries work on a chemical reaction to produce electricity. Phillipe’s research discovered that the chemical reaction works best with warmth, and worse when it’s cold. So when a battery is low, it might still produce enough electricity to keep going when it’s warm. But at night, as the temperature dips, a weak battery can start to give out, and hence, the 2 am chirp.

This is the same reason parents may find their kid’s battery-powered toys may suddenly make noise at 2 am as well.

Additional information

After 2o14, all new smoke detectors should have a 10-year battery.

Smoke detectors installed after 2015 should have installation dates written on them so you know when to change them.

To book your home inspection, call 818-298-3405.