Best Buy offers the Samsung SmartThings ADT Carbon Monoxide Alarm for $9.99. Choose in-store pickup to avoid the $5.49 shipping fee. That's tied with our mention from a week ago and the lowest price we've seen. (It's the best deal now by $6.) It can send alerts to your smartphone via the SmartThings Mobile app.
Reviewing this critical insurance policy takes a little effort, but it pays off big.