First Alert Carbon Monoxide Detector CO400 + Plug-in Battery Backup CO Alarm $17

First Alert Carbon Monoxide Detector CO400 + Plug-in Battery Backup CO Alarm $17.06. Amazon has First Alert Carbon Monoxide Detector CO400 + CO605 Plug-in Battery Backup CO Alarm for $18.96 -> Now $17.06. Shipping is free with Prime or on $35+ orders.