Every ADU must pass a smoke and carbon-monoxide detector inspection before occupancy. LADBS records show a 22.6% first-time fail rate in the City of Los Angeles, from 15,786 inspections over the trailing 12 months.
22.6%
of ADU Smoke & CO Detector inspections fail on the first attempt in City of Los Angeles
Based on 15,786 first-attempt inspections, Trailing 12 months (2025-07-01 → 2026-07-01).
A first attempt counts as a failure when it drew a correction notice or the work was not ready when the inspector arrived.
Source: LADBS (9w5z-rg2h).
This is one of the more forgiving inspections in the ADU sequence: the requirements are well defined, and most projects pass the first time. Failures usually come down to placement, power source, or interconnection details rather than anything structural.
Why Smoke & CO Detector inspections fail
Wrong placement
Detectors too close to kitchens or bathrooms (nuisance-alarm zones), too far from sleeping areas, or missing from a required room are the most common corrections.
Missing interconnection
Code generally requires detectors to be interconnected so that one alarm triggers all. A non-interconnected install fails.
Power-source issues
Hard-wired detectors with battery backup are typically required in new construction; battery-only units where hard-wiring is required will be flagged.
Missing CO coverage
Carbon-monoxide detection is required near sleeping areas in units with fuel-burning appliances or an attached garage; leaving it out triggers a correction.
How to pass on the first attempt
Install detectors in every bedroom, outside each sleeping area, and on every level.
Confirm CO detection where fuel-burning appliances or an attached garage exist.
Verify detectors are hard-wired with battery backup and interconnected.
Keep detectors the required distance from cooking and bathroom steam sources.
Test every unit before the inspection.
What the inspector checks
The inspector confirms that smoke and carbon-monoxide detectors are present in every required location, correctly powered, interconnected, and functional — the baseline life-safety layer before occupancy.
What a failure costs you
Corrections here are usually quick and inexpensive to fix, but they still require a re-inspection, which can add days to the schedule. Because detectors are checked late, a failure can hold up the final sign-off.
Frequently asked questions
In each bedroom, outside each sleeping area, and on every level of the unit. Exact placement follows the current California Residential Code and local amendments.
Yes, where the unit has fuel-burning appliances or an attached garage. CO detection is required near sleeping areas in those cases.
In new construction they generally must be hard-wired with battery backup and interconnected. Battery-only units are usually not sufficient.
Most often placement, missing interconnection, or a missing CO detector — not the devices themselves. See the common reasons above.
From LADBS public inspection records for the City of Los Angeles, recomputed weekly over a rolling 12-month window.
Source & methodology
ADUscale Research
This figure is a first-time pass rate — the share of permits whose first
attempt at this inspection type passed — computed directly from LADBS public inspection
records (9w5z-rg2h)
for the City of Los Angeles, over a rolling trailing 12 months, refreshed weekly. We only
count each permit's first attempt, so it shows how often work passes the first time.
A first attempt is a fail if it drew a correction or the work was not ready when the
inspector arrived. Data source and methodology:
LA ADU Inspection Index ·
InspectPilot.
Last updated: July 1, 2026 · Geography: City of Los Angeles
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