Avantek via Amazon offers the X-Sense Smoke/Heat Detector and Fire Alarm
, model no. CC03M1, for $17.99. Coupon code "KMLYQ946" cuts it to $10.79
. Plus, Prime members bag free shipping
. (Non-members can spend $35 or more to qualify for free shipping; otherwise, shipping costs $6.77.) That's $29 off list and the lowest total price we could find. Features include twin sensor technology that detects both smoke and heat, an 85-decibel fire alarm, and test/reset button. It requires one 9-volt battery, included.