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Building Code Reference

Got a CRC R310.4 correction?

Smoke alarm interconnection

For builders in California, Greater Seattle, the Las Vegas area, the Denver area and Kansas City · CrossBeam Permits

What this code requires, how to fix it, and how cities and counties review it

What this code requires

CRC R310.4 is the California Residential Code section that requires all required smoke alarms in a dwelling to be interconnected so that when any one activates, all alarms sound simultaneously. Alarms must be hardwired to the building electrical system and include a battery backup. Interconnection may use hard-wired circuits or wireless technology listed for that purpose. Most single-family residential and ADU permits get flagged on R310.4 when the plans don't show interconnection wiring or specify a listed wireless system.

How to fix it

  1. Add interconnection notation to the electrical plans

    On your electrical floor plan, add a note that reads: "All smoke alarms to be hardwired and interconnected per CRC R310.4. Provide battery backup on each unit." List the circuit number or panel designation that will serve the smoke alarm branch circuit. This is the single most common missing piece and often the only correction you need to clear.

  2. Show the interconnection circuit in the panel schedule

    Add a dedicated row to your electrical panel schedule for the smoke alarm circuit. Label it clearly: "Smoke Alarms — Interconnected, CRC R310.4." Include the breaker size (typically 15A), wire gauge (minimum 14 AWG), and the rooms served. Some plan-checkers accept a floor-plan note referencing the circuit; others want it in the schedule. Put it in both to avoid a second round.

  3. Verify every required alarm location is on the interconnected system

    Cross-check your floor plan smoke alarm symbols against CRC R310.3 required locations: inside each sleeping room, outside each sleeping area, and on each story including the basement. Every symbol must tie to the same interconnected circuit or the same listed wireless network. If any alarm is shown as a standalone battery-only unit, correct it. R310.4 applies to all required alarms, not just some of them.

  4. Specify a listed wireless system if not using hard-wired interconnection

    If you're using wireless interconnection instead of running new wire, the plans must state that the system is listed for that purpose. Add a note: "Wireless smoke alarm interconnection system to be listed per UL 217 or equivalent listing for wireless interconnection." Include the manufacturer name or model series if known. Generic references to "wireless smoke alarms" without a listing callout will not pass plan check.

  5. Address existing alarms on remodels and additions

    For remodels or room additions, document how existing smoke alarms will be handled. If the existing system is already hardwired and interconnected, add a note: "Existing smoke alarm system is hardwired interconnected; new alarm to be added to existing circuit." If the existing system is battery-only standalone units, the correction may require upgrading the entire dwelling. Show the upgrade scope on the electrical plans so the plan-checker can see the full picture.

  6. Confirm battery backup notation on each hardwired unit

    Each hardwired smoke alarm must include integral battery backup for power outages. Add a callout or specification note: "All hardwired smoke alarms to include integral battery backup per CRC R310.6." This is standard on most combination units, but the plans need to state it. If you're specifying a model number, verify the model includes battery backup in its listing.

  7. Write a point-by-point response letter when resubmitting

    When you resubmit, attach a written response to each item in the corrections letter. For R310.4 items, cite the plan sheet and detail where each correction was addressed. Example: "R310.4 — Interconnection notation added to Sheet E1 Note 3. Panel schedule updated on Sheet E2." Plan-checkers process dozens of sets at once. A clear response letter cuts review time and reduces the chance of a third round.

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Why you got flagged

Plan-checkers flag R310.4 most often because the electrical plans don't show interconnection at all. When a set of plans shows smoke alarm locations on the floor plan but the electrical sheet has no notation about interconnection wiring or a listed wireless system, the plan-checker has no way to verify compliance. This is the most common scenario — the smoke alarms are there, but the plans treat them as standalone battery units rather than a coordinated system.

A second common flag happens on remodels and additions. When a contractor adds a bedroom or converts a space, the permit requires bringing the existing smoke alarm system up to current code. Plans that show only a new alarm in the added space, without indicating how it ties into or replaces the existing system, will get a correction. The plan-checker needs to see that the whole dwelling meets R310.4, not just the new addition.

The third scenario involves panel schedules and electrical load calculations. Even when interconnection is shown on the plans, some plan-checkers will flag the circuit if it isn't listed in the panel schedule or if the branch circuit isn't clearly labeled for smoke alarms. Without that documentation, the inspector has no way to confirm the circuit was installed per the plans.

Wireless interconnection systems are allowed under R310.4, but the plans must specify that the system is listed for the purpose. "Wireless smoke alarms" without a listing reference or manufacturer callout will get flagged. The plan-checker can't assume a wireless system meets the interconnection standard without that documentation.

The official code

California Residential Code Title 24 Part 2.5 — Official Adopted Code Text (DGS Building Standards Commission)

Read the source →

Common questions

Does R310.4 apply to ADUs?
Yes. An ADU is a separate dwelling unit and must have its own interconnected smoke alarm system per CRC R310.4. The ADU alarms don't need to be tied to the main house alarms — they function as a separate independent system. All alarms within the ADU must be hardwired and interconnected with battery backup. If the ADU is detached, it needs an electrical connection to power the smoke alarm circuit. Some contractors assume small battery-only alarms are acceptable for compact ADUs; that assumption will get the permit flagged every time.
Can I use wireless smoke alarms instead of running new wire?
Yes, wireless interconnection is allowed under CRC R310.4 as long as the system is listed for that purpose. You can't use just any wireless smoke alarm and assume it qualifies. The system must be specifically listed for wireless interconnection — look for UL 217 or a manufacturer's listing statement that explicitly covers wireless interconnection. On your plans, call out the system by manufacturer or model series and note it's listed for wireless interconnection. Wireless is useful on remodels where running new wire through finished walls is impractical.
What if the existing house has battery-only alarms — do I have to replace them all for an addition?
Possibly. When a permit triggers a smoke alarm upgrade, the whole dwelling typically must meet current code, not just the new addition. If existing alarms are battery-only standalone units, adding a bedroom will generally require upgrading the entire system to hardwired interconnected. The scope depends on the permit type and extent of work. Some jurisdictions have more lenient interpretations for minor alterations. Check with your plan-check counter before assuming a partial upgrade will pass. Including the full upgrade scope in your original submittal is the cleaner path — it avoids a correction letter and the 60-day wait to find out what they need.
Does the smoke alarm circuit need a dedicated breaker?
No, CRC R310.4 doesn't require a dedicated breaker for smoke alarms. The alarms can share a branch circuit with other loads such as lighting. The key requirement is that the circuit is identified in the panel schedule and on the plans. Some inspectors prefer dedicated circuits for clarity, and a few jurisdictions have local amendments requiring it. If you're uncertain about your city's interpretation, a dedicated 15A circuit for smoke alarms is a minor cost that eliminates the ambiguity entirely.
Do smoke alarms in garages need to be on the interconnected system?
CRC R310.4 requires interconnection for required smoke alarms. Garages are not a required smoke alarm location under CRC R310.3, so a garage alarm is not a required alarm and doesn't need to be wired into the interconnected system. If you choose to install one in the garage, including it in the system is cleaner but not mandatory. Carbon monoxide alarms required near attached garages under CRC R311 are separate devices governed by different provisions — don't confuse CO alarm requirements with smoke alarm interconnection.
What's the difference between R310.3 and R310.4 on a corrections letter?
R310.3 covers where smoke alarms must be located: inside each sleeping room, outside sleeping areas, and on each story. R310.4 covers interconnection: all required alarms must sound together. Power (hardwired with battery backup) is R310.6. A corrections letter can cite them together: R310.3 when required locations are missing from the plans, R310.4 when interconnection documentation is missing, R310.6 for power. Fixing both in a single resubmittal is the goal. Check your plans for both location coverage and interconnection documentation before you send anything back.

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