Smoke and Carbon Monoxide Alarms When Selling a House in Washington (2026)

Short answer: If you’re selling a house in Washington, plan to have working carbon monoxide alarms and at least one smoke detection device in place before the buyer moves in. State law puts both on the seller. The carbon monoxide rule, RCW 19.27.530, applies to sales on or after July 26, 2009. The smoke detection rule, RCW 43.44.110, applies to homes sold on or after July 1, 2019. Form 17 asks about both, so you’ll answer the question in writing early in the sale.

This is general information, not legal advice. Your city or fire department may have its own rules, and a licensed electrician can tell you what your house needs.

What Washington law requires of sellers

Carbon monoxide alarms. RCW 19.27.530 required the state building code council to adopt carbon monoxide alarm rules for residential buildings. Owner-occupied homes legally occupied before July 26, 2009 are exempt from the general phase-in. But the same subsection says that when one of those homes is sold on or after July 26, 2009, the seller must equip it with carbon monoxide alarms in line with the state building code before the buyer or anyone else may legally occupy it.

Smoke detection devices. RCW 43.44.110 says that for any dwelling unit sold on or after July 1, 2019 that doesn’t have at least one smoke detection device, the seller must provide at least one before the buyer or anyone else occupies it. A few other parts of that section are worth knowing:

• A violation doesn’t affect the transfer of title, ownership or possession.
• Interconnection isn’t required, where it isn’t already present, for repairs made solely as a condition of sale.
• Any owner, seller or tenant who doesn’t comply can be fined up to $200. An owner can be fined $5,000 if, after the failure, a fire causes property damage, injury or death to a tenant or a member of a tenant’s household.
• Enforcement happens after a fire, by the fire chief in a city or town or by the county fire marshal or other designated fire official in unincorporated areas.

Both statutes say licensed real estate brokers aren’t liable for a seller’s failure to comply. The job is yours, not your agent’s or the buyer’s.

Smoke vs. carbon monoxide at a glance

Based on: RCW 19.27.530, RCW 43.44.110, WAC 51-51-0314, WAC 51-51-0315 and RCW 64.06.020 (Form 17), Washington State Legislature.

Where the alarms go

RCW 19.27.530 points to the state building code, and RCW 43.44.110 points to the state building code and the state fire protection rules. The Washington residential code sections are a good guide to placement.

Data from: WAC 51-51-0314 and WAC 51-51-0315 (Washington residential code R314 and R315), Washington State Legislature. Your city or county building department enforces the code and may add local requirements.

Fitting it into your sale

Check the alarms when you prep the house, not the week of closing. If you’re doing a pre-listing inspection, ask the inspector to note alarm locations. If the house has a gas furnace, gas water heater, attached garage or a wood stoves and fireplaces setup, think carefully about carbon monoxide alarm locations. Combination alarms can cover both needs in some spots.

When you fill out Form 17, items 5E and 5F ask whether the home has carbon monoxide alarms and smoke detection devices, and each comes with a note citing the statute. RCW 64.06.020 currently has two versions on the Legislature’s site: one marked effective until January 1, 2027, and one effective January 1, 2027. The questions quoted here appear in both. If your sale runs across the new year, check which form is being used.

Even if you’re selling a house as-is, the alarm duties still apply. They’re part of what the law expects before the buyer occupies, so put them on the same list as your other closing process tasks. If you’re selling with a tenant in place, remember the tenant maintains the alarms and you, as owner, install them. The cost of a few alarms is small next to the other line items in the true cost of selling a house in Washington.

FAQ

Do I have to install carbon monoxide alarms before I sell my house in Washington?

Yes, in nearly every sale. RCW 19.27.530 exempts owner-occupied homes legally occupied before July 26, 2009 from the general requirement, but if such a home is sold on or after that date, the seller must install carbon monoxide alarms that meet the state building code before the buyer can legally occupy the home.

Do I have to install smoke alarms before I sell?

If the home doesn’t have at least one smoke detection device, yes. Under RCW 43.44.110, for any dwelling unit sold on or after July 1, 2019 without one, the seller must provide at least one before the buyer occupies it. Missing it doesn’t affect the transfer of title, but the law sets a fine of up to $200, and $5,000 in some cases after a fire.

Where do carbon monoxide alarms go?

Under the Washington residential code (WAC 51-51-0315), outside each separate sleeping area near the bedrooms and on each level of the home, following the manufacturer’s instructions. If a fuel-burning appliance is in a bedroom or its attached bathroom, an alarm goes in that bedroom too.

Do the smoke alarms have to be hardwired and interconnected?

For a sale-only fix, not necessarily. RCW 43.44.110 says interconnection isn’t required where it isn’t already present when repairs are made solely as a condition of sale. The code (WAC 51-51-0314) does call for interconnected alarms in new work, allows listed wireless alarms to meet that, and allows battery power for alarms added to existing homes under its alterations section.

Will my agent make sure the alarms are in?

Your agent can remind you, but the duty is the seller’s. RCW 19.27.530 and RCW 43.44.110 both say licensed real estate brokers aren’t liable for a seller’s failure to comply. Form 17 also asks you directly, in items 5E and 5F, whether the home has carbon monoxide alarms and smoke detection devices.

Talk it through with a local agent

Peter Kim and Odigo Real Estate Club can walk you through the pre-listing checklist, Form 17 and the steps before closing, with 25+ years combined experience, 593+ closings, and 122 five-star Zillow reviews. See our home selling services or ask for a property valuation.

Odigo Real Estate Club · REAL Brokerage, WA #112064 · 16108 Ash Way, Suite 201, Lynnwood, WA 98087 · (425) 409-3823 · Mon–Sat 9 AM–6 PM, closed Sunday

Sources

• Washington State Legislature, RCW 19.27.530 (carbon monoxide alarms; seller duty for sales on or after July 26, 2009), https://app.leg.wa.gov/RCW/default.aspx?cite=19.27.530 , accessed Nov 4, 2026.
• Washington State Legislature, RCW 43.44.110 (smoke detection devices; seller duty for sales on or after July 1, 2019; fines), https://app.leg.wa.gov/RCW/default.aspx?cite=43.44.110 , accessed Nov 4, 2026.
• Washington State Legislature, WAC 51-51-0315 (Washington residential code Section R315, carbon monoxide alarms), https://app.leg.wa.gov/wac/default.aspx?cite=51-51-0315 , accessed Nov 4, 2026.
• Washington State Legislature, WAC 51-51-0314 (Washington residential code Section R314, smoke alarms), https://app.leg.wa.gov/wac/default.aspx?cite=51-51-0314 , accessed Nov 4, 2026.
• Washington State Legislature, RCW 64.06.020 (seller disclosure statement form; version effective until Jan 1, 2027 and version effective Jan 1, 2027), https://app.leg.wa.gov/RCW/default.aspx?cite=64.06.020 , accessed Nov 4, 2026.