Wholesale Home Improvement Products offers the Kidde i9010 Smoke Detector, model no. 21008697, for $17.99. Coupon code "dealnews1" cuts it to $14.99. With free shipping, that's the lowest total price we could find by $8, excluding the below mention. It features a built-in Li-ion battery that lasts up to 10 years, ionization sensing technology, and Smart Hush button that can silence false alarms.
A close price: Amazon offers it for $16.95 with free shipping for Prime members.