Yes. Washington State law (RCW 19.27.530) requires Carbon Monoxide detectors in all homes being sold, regardless of year built.
They must be installed **before closing** and before the buyer takes possession.
– Minimum: One per floor, including the basement.
– Placement: Ideally outside sleeping areas and on each level of the home.

If not installed, the seller can be liable — appraisers also commonly call this out as a requirement.

Yes. Washington State requires working smoke alarms in all homes on every level and inside/outside sleeping areas.
– Must not be disconnected or missing batteries.
– If the alarm is older than 10 years, replacement is recommended.

*Special note:* If the home has a detached ADU, smoke alarms are required there as well.

Yes. Washington State requires water heaters to be **double-strapped** to resist earthquake movement.
This applies to both gas and electric water heaters.
Missing/loose straps are a common appraiser callout and can delay closing if not corrected.

Not always. Battery-powered units are acceptable unless local building code or remodeling permits require hardwiring.
Smart combo units (CO + smoke) are allowed as long as they meet UL standards.

Usually no formal documentation is required.
However, real estate contracts require the seller to certify that CO detectors are installed before buyer possession.
Occasionally, an appraiser or inspector may require a photo for proof.

The appraiser (especially on FHA/VA loans) will mark them as required repairs.
If not corrected, it can:
– Delay loan approval
– Delay closing
– Require a re-inspection, costing the seller additional money

No. Sellers can self-install CO detectors, smoke alarms, and water heater earthquake straps as long as:
– They are installed correctly, and
– They are functional at the time of closing.
Home Depot or Lowe’s units are acceptable and inexpensive.