What this code requires
CRC R310.6 is the California Residential Code section that requires smoke alarms to be powered by the building's electrical wiring and backed up by a battery. The alarm circuit must be unswitched — it cannot share a circuit controlled by a wall switch that could cut power to the alarm. Most residential permits, including ADUs and remodels that add or relocate sleeping areas, get flagged on R310.6 when the electrical plans don't specify hardwired alarms on a dedicated, unswitched circuit with battery backup.
How to fix it
Confirm the alarm type on the electrical plans
Pull up your electrical plans and check the smoke alarm symbol legend. The note must say 'hardwired smoke alarm with battery backup' or equivalent. If it says 'battery-operated,' lists only a battery voltage, or leaves the power source blank, that's your correction. Every smoke alarm on the plan needs to show the correct type. Mark the change before anything else — the rest of the fix hangs on getting this callout right first.
Verify the circuit is unswitched from panel to alarm
Trace the smoke alarm circuit on the panel schedule and the floor plan wiring diagram. The circuit feeding all smoke alarms must run directly from a breaker to the alarm(s) with no wall switch, timer, occupancy sensor, or smart switch anywhere in between. If the plans show a switch on that circuit, reroute the alarm feed to a dedicated breaker or an always-hot branch circuit. Document the change on the panel schedule and update the circuit legend. Label the breaker 'Smoke Alarms — Unswitched' so the plan-checker can verify it at a glance.
Add a battery backup callout to the electrical schedule
R310.6 requires both primary AC power and battery backup. Even if the alarms you're installing physically have a battery slot, the electrical plans must say so explicitly. Add a general note or spec table entry: 'Smoke alarms: 120V AC primary power, battery backup per CRC R310.6.' If the project uses a specific alarm model, list it by model number in the electrical schedule with the backup type noted. The plan-checker needs the callout in writing and won't approve what the drawings don't show.
Confirm the alarm is listed for AC power with battery backup
Not all smoke alarms are dual-power listed. The alarm must be listed and labeled to UL 217, and California State Fire Marshal listed, for use with both primary AC power and battery backup. Pull the cut sheet for the model you plan to install and verify the listing. If your current spec shows a battery-only model, swap it to a dual-power listed model and update the submittal. Attach the cut sheet to the resubmittal package so the plan-checker can confirm the listing without back-and-forth.
Check interconnection wiring if alarms are required to be linked
If your project requires interconnected smoke alarms (most new construction under R310.4), check that the interconnect wire is not on a switched circuit either. The typical three-wire smoke alarm hookup uses black for line, white for neutral, and red for the interconnect signal. All three must feed from an always-on circuit. If you're using wireless interconnect alarms, each alarm still needs its own AC power feed per R310.6 — the wireless signal doesn't substitute for wired power. Note the wiring method on the plans with references to both R310.4 and R310.6.
Submit corrected electrical sheets with a revision cloud and response letter
Redline the affected electrical sheet (typically E-1 or E-101), cloud all smoke alarm circuit changes and the general note additions. Bump the sheet revision and re-upload if your city uses an electronic submittal portal. Include a correction response letter that states: 'Correction: Smoke alarms revised to hardwired 120V AC with battery backup on an unswitched circuit per CRC R310.6. See Sheet E-1, revision cloud A.' A clear response letter lets the plan-checker close the correction in one pass rather than routing it back for clarification.
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Why you got flagged
Here's why plan-checkers flag R310.6: the most common corrections come in four situations, and most are avoidable with a single note on the electrical plans.
The first is battery-only alarms on new construction. If your electrical plans show smoke alarms with no power source noted, or if the alarm spec sheets list only a 9-volt battery, that's an automatic correction. New residential construction has required hardwired alarms for decades, but battery-only alarms still slip through when contractors spec the hardware before checking the plan requirements.
The second is alarms wired on a switched circuit. Smoke alarms cannot be on a circuit that a wall switch can interrupt. A common mistake: running the smoke alarms off the same circuit as a bathroom exhaust fan or hallway light. The plan-checker reads the circuit diagram, sees the switch, and sends the plans back. R310.6 is clear that the power feed must be always-on: no switch, no timer, no occupancy sensor can sit between the breaker and the alarm.
The third is missing battery backup specification. The plans may show hardwired alarms but say nothing about backup power. R310.6 requires both primary hardwired power and a battery that keeps the alarm running during an outage. If the plans don't call out battery backup explicitly, the plan-checker won't assume it's there. Add a one-line note to the electrical schedule: 'Smoke alarms: 120V AC primary with battery backup per CRC R310.6.'
The fourth is remodels that add sleeping areas. Converting a bonus room to a bedroom, or finishing a basement with a sleeping alcove, triggers new smoke alarm requirements under current code. Contractors sometimes tie new alarms into existing wiring on a switched loop. That shortcut creates a correction even on an otherwise clean set of plans.
The official code
California Residential Code R310.6 — Smoke Alarm Power Source (California Code of Regulations, Title 24, Part 2.5)
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