Walk the house with a clipboard and a step stool. Every smoke alarm has a manufacture date printed on its back or side. Write each one down next to its location. That date is a planning input. It tells you when to schedule a replacement, the same way a filter date tells you when to change a filter. It is not a sign that the unit has failed.
The upkeep you can do yourself is straightforward. Press the test button on each unit on a regular schedule and listen for a full, clear sound. Replace batteries on the schedule the maker prints in the manual, and do it on the same day you test. Vacuum the vent slots gently with a soft brush attachment. After any battery swap, test the unit again before you leave the room. Keep a short log in a notebook or on the fridge with the date of each test and the battery change.
Some work belongs to someone else. Hand it off when an alarm is wired into the house circuit, because that wiring is not a homeowner task. Hand it off when a unit does not respond to a fresh battery, when a backup battery will not seat, or when you want to add units that are tied together so one sounding sets off the rest. A licensed electrician can check whether the existing wiring is interconnected, whether each unit sits where the maker's placement guidance says it should, and whether a replacement matches the sounder type of the set already in place.
Before you call anyone, gather the facts. Write down the brand and model, the manufacture date, whether each unit is battery only or hardwired, and whether the units talk to each other when one sounds. Ask the person you hire what they will test, whether they will leave a written record of each unit, and whether a permit or inspection applies in your area. Your local building department can tell you what applies where you live.
When you buy a replacement yourself, match the sounder type and the interconnect setup of the existing set. Read the package for placement and replacement guidance before you open it. When a unit reaches its manufacture-date planning point, put the replacement on the calendar that day, the same way you would plan any other household system.