Voted Best Smoke/ Carbon Monoxide Detector, the Roost Smart Battery. plugs into any existing smoke or CO2 detector and makes it a smart device… for $35.
Now, when your alarm goes of, it will alert you (and others) on your smartphone, from where you can either call 911, or silence the alarm, in case a piece of burnt toast is to blame.  This is a simple, affordable, andeffective way to retrofit all smoke detectors into a superior product.
Roost also makes a 2 in 1 alarm (smoke & fire) and a 4 in 1 alarm (smoke, fire, carbon monoxide, and natural gas) that are Wi-Fi enabled (see below).    Features include low battery detection (no 3 am chirps), alerts sent you smartphones, and the ability to notify family members in case of an emergency.