Amazon has the Kidde Carbon Monoxide Detector, Plug In with Battery Backup, CO Detector, model no. KN-COP-DP2, for $13.04 (regularly $29.99) with Free Shipping for a limited time.

CO detector that alerts with a warning signal against dangerous levels of carbon monoxide in your home. Easy & quick installation – plugs directly into your home’s standard wall outlet, 85 decibel alarm alerts of fire. Protects during a power failure – 2-AA batteries, included with pack, provide backup service in the event of a power outage.