Jefferson County, MO Fire Regulations: Smoke Detectors (2026)
Key Facts
- Power source
- 120V AC, hardwired, with battery backup
- Battery-only exception
- Homes without commercial power
- Wiring rule
- No disconnecting switch other than breaker
- Related rule
- CO alarms share same power standard
- Governing section
- § 500.400, amending IRC § R314.6
Summary
Smoke alarms in Jefferson County homes must be hardwired to 120-volt AC power with battery backup whenever the building has commercial electric service, under the county's amendment to IRC Section R314.6. Only homes without commercial power, or alarms installed under the code's remodel exception, may run on batteries alone.
R314.6. Delete and insert in lieu thereof the following: Power Source. Smoke alarms shall receive 120V/AC from the building wiring where such wiring is served from a commercial source and, where primary power is interrupted, shall receive power from a battery. Wiring shall be permanent and without a disconnecting switch other than those required for overcurrent protection. Exceptions: 1. Smoke alarms shall be permitted to be battery operated where installed in buildings without commercial power. 2. Smoke alarms installed in accordance with Section R314.2.2 shall be permitted to be battery powered.
Full Breakdown
Jefferson County's amendment to IRC Section R314.6 sets the power source for required smoke alarms: they must receive 120-volt AC power from the building's permanent wiring wherever that wiring is served from a commercial power source, and must switch to battery power if the primary electrical supply is interrupted. The wiring feeding the alarm has to be permanent, with no disconnecting switch other than the overcurrent protection the circuit itself requires, so a homeowner cannot wire an alarm to a switched outlet or breaker that gets turned off.
Two exceptions carve out battery-only alarms: smoke alarms are allowed to run on batteries alone in buildings that have no commercial power at all, and alarms installed under the separate remodel provisions of Section R314.2.2 may likewise be battery-powered rather than hardwired. Because the power-source rule sits inside the same Article III amendments as the county's carbon monoxide alarm power rule in R315.5, both devices are typically installed and inspected together, with hardwiring and interconnection checked as part of the same final inspection required before occupancy under Section 500.350.
Violations & Fines
Installing a smoke alarm on battery power alone in a home with commercial electric service, outside the code's two exceptions, is a Building Code violation under Section 500.300, a misdemeanor punishable by a fine up to one thousand dollars, imprisonment up to one year, or both. The Code Official can refuse final inspection approval under Section 500.350 until the alarm is properly hardwired with battery backup.
Frequently Asked Questions
Can I use a battery-only smoke alarm in my Jefferson County home?
What kind of circuit can a hardwired smoke alarm be on?
Do inspectors check smoke alarm wiring before I can move in?
Sources & Official References
Other rules in Jefferson County
Compare Jefferson County to another location·View the Missouri fire regulations overview
See something wrong?
Help us keep this page accurate. If you notice an error or outdated information, let us know.