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.
The dollar store is the most amazing place to find bargains for certain purchases. Yes, even pregnancy tests.