We have started switching all our old smoke detectors out fo these. They usually cost around $20 a piece so this is a great deal. They last 10 years and you NEVER have a chirping battery to replace.
Code One 10-Year Sealed Battery Smoke Detector with Ionization Sensor (6-Pack) $79.99 (reg $99.99)
They also have one with built-in Carbon Monoxide Detectors too. Check out the entire sale HERE.