Amazon: SIX First Alert Hardwired Smoke Detectors with Backup Battery . $45.49

Amazon is offering this SIX First Alert Hardwired Smoke Detectors with Backup Battery for $45.49 shipped (regularly $58.32)! --- only $7.58 each.
These smoke detectors are equipped with an ionization sensor that helps to reliably detect smoke from fast-flaming fires and then alert you with an 85-decibel alarm. It is simple to use, with a single test/silence button, and side-load battery compartment.