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 $10 under our January mention 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.
Vinegar is arguably the most versatile product in your house. If you aren't using it for all of these purposes, you're probably wasting money.