Oregon Revised Statutes §455.360:
New and existing one-, two- and multi-family dwellings, rental dwellings, and Group R occupancies (hotels, motels, dormitories) that contain sources of CO must install a minimum of one CO detector per building and cover all sleeping areas. (Effective date: April 1, 2011)

Lays out requirements for 1 or 2 family dwellings and multi-family dwellings regarding CO alarms when transferring title