Carbon monoxide detectors? Say what? Yup, on April 1, 2012 there is a new Washington State Point of Sale Mandate requiring these to be in single family residential properties sold. (thanks to Wolf Puls, Seattle King County Realtor President for bringing this to my attention.)
In pertinent part RCW 19.27.530 says, "Owner-occupied single-family residences legally occupied before July 26, 2009, are exempt from the requirements of this subsection (2). However, for any owner-occupied single-family residence that is sold on or after July 26, 2009, the seller must equip the residence with carbon monoxide alarms in accordance with the requirements of the state building code before the buyer or any other person may legally occupy the residence following such sale." Looks like there may have been slight delay in getting this implemented.