Manufacturers recommend that you replace your smoke detectors every ten years, which is recent news to me. This came up because one of mine started chirping, which is a sign that it's on the fritz. I tried web-surfing for a model that was compatible, and couldn't find one, so I called the company who bought the company that manufactured mine. They said that no current models were compatible, so I'd have to replace the wires and mounting plates. That's not a bad job, just three wires, about as hard as replacing a flush-mount light fixture. He also asked me to read the model number on mine. It turns out, they were made in 1989, and were beyond their 22nd birthday.
So, I've replaced all eight of them, in my house. Not a big deal; five minutes work and about $30 each. My ears are ringing a bit from the tests, which my children and beagle were certainly not shy about expressing how much they detested the process, but it's done.
These are a bit of an upgrade, and we're less likely to be awoken at night by more chirping.
So, you might check the dates of your smoke detectors. It might be printed inside the unit, or follow the manufacturing code of my Firex ones. For a code printed like 89163, in the above photo, the first two numbers indicate the year of manufacturer.