While I was sleeping at my daughter's apartment, near midnight on Halloween, I was awakened by the sound of a fire alarm. I recognized that sound from the monthly fire drills that I pull at work. It was only a few years ago that my daughter lost everything she owned when her father's apartment complex burned to the ground due to bad wiring and inadequate fire alarms. My daughter was sleeping right through the apartment complex fire alarm because she's hard of hearing, so I woke my daughter up and told her to get dressed; we were going outside. It turned out later to be a false alarm, and no damage was done.
The biggest problem with smoke alarms is that people will install them but forget to check the batteries to make sure they're all still working, so the first thing I did when I got home from D.C. was check on all of my own smoke alarms. The Kidde i12060 Smoke Alarm is wired in to my house, so as long as the power to the house is still on, the smoke alarm will still work. But just in case the power goes out to the house, there is a 9V battery back-up in the Kidde i12060 Smoke Alarm. The smoke detector will chirp when the battery runs low, and the 9V battery is very easy to replace just by pressing the tab on the front of the smoke detector. The ionization sensing technology can detect the invisible fire particles that are associated with flaming fires, but these smoke detectors are best used in conjunction with a photoelectric sensing alarm that can detect smoldering fires. The Kidde i12060 Smoke Alarm has an 85dB level at 10', about twice as loud as my alarm clock is, and it's not something that I'm likely to sleep through if it goes off.