Do ADUs require smoke detectors?

Yes. A California ADU is a separate dwelling unit, so the California Residential Code requires both smoke alarms and carbon monoxide (CO) alarms in the unit, and their locations must be shown on the electrical plans. This is a code requirement, not an upgrade — units without them will not pass inspection.

Where smoke alarms are required

Smoke alarms are generally required in each of the following locations within the ADU:

• Inside each sleeping room (every bedroom).
• Outside each sleeping area, in the immediate vicinity of the bedrooms (hallway or adjacent space).
• On each story of the unit, including basements and habitable attics.

Where more than one alarm is required, they generally must be interconnected, so that when one sounds, they all sound. New construction typically requires hardwired alarms with battery backup; alterations and conversions may have different allowances — confirm what applies to your project.

Where carbon monoxide alarms are required

CO alarms are required when the dwelling contains a fuel-burning appliance, a fireplace, or an attached garage. They are generally placed:

• Outside each separate sleeping area, in the immediate vicinity of the bedrooms.
• On each story of the dwelling, including basements.

An all-electric ADU with no fuel-burning appliances and no attached garage may not strictly require CO alarms — but because many ADUs share a site with a garage or use combination smoke/CO devices, they are very commonly included. Verify your specific configuration with your building department.

How it shows up on the plans

On our electrical plans, every required smoke and CO alarm is located on the floor plan with a symbol in the legend, and the general notes call out the interconnection, hardwiring, and battery-backup requirements per the applicable code edition. Missing or unlocated alarms is a routine plan-check correction we head off before submittal.

Why garage conversions need special attention

Converting a garage into an ADU is one of the most common scenarios, and alarms are a frequent legalization correction because the original space was never built as living quarters. When the conversion creates a new sleeping room and removes the garage, the unit still needs full smoke-alarm coverage in and around the new bedroom and on each story. If the converted ADU is now attached to a remaining garage or contains any fuel-burning appliance, CO alarms come back into play. Older unpermitted conversions also commonly lack the interconnection and hardwiring that current code expects — all of which we resolve on the plan set up front.

Requirements vary by jurisdiction and code cycle — placement, interconnection, and hardwiring rules can differ for new construction versus garage conversions and alterations. Confirm with your local building department.

Smoke and CO alarm placement is included in every electrical set at no extra charge, and two revisions plus city corrections are part of every order. See how it works or order to begin.