QVC offers the Ring Alarm Smoke and CO Listener for $29.99. Coupon code "TAKE10" drops that to $19.99 for first time customers. With $3.50 for shipping, that's the best deal we could find by $12. (Even without the coupon, it's still a low by $2). It's compatible with the Ring Base Station allowing setup and connectivity through the Ring App, provides real-time notifications, and does not detect fire, smoke or carbon monoxide.

Note: This item is currently waitlisted and will ship within 45 days if stock returns, and can still be purchased for the above price.