Amazon offers the Kidde Battery-Operated Carbon Monoxide Alarm, model no. KN-COPP-B-LPM, for $20.25. At checkout, it drops to $16.20. Plus, Prime members bag free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, it adds $6.74.) That's a slight drop since our May mention and the lowest total price we've seen. (It's currently $4 below the lowest price we could find for an alarm for pickup.) It features a backlit display and requires three AA batteries (included).