Kirk, you bring up an excellent point, smoke alarms don't work without power.
A few years back I converted all of mine to hard-wired 120 volt models. They have a small rechargeable battery pack kept topped up by the house power, and which powers them in the case of a power failure.
Another big advantage of these detectors is that they are connected together, if one goes off, they all go off. Particularly handy if the one that trips is in the back of the basement and you are 3 floors up in the front of the house asleep.
In my case they also interconnect to my house alarm system, if one goes off it trips the 'panic' function of the alarm system, this turns on the power failure lighting inside and the strobe and siren on the outside of the house.
In the one case I needed it, luckily for a very minor problem, it made a) getting out of the house, and b) the fire dept. finding the house, much faster & easier!
BTW, the 'minor' problem was a raccoon trying to warm his butt in the chimney, this caused the smoke to back up into the house and trip the smoke alarm.