Dad will tell you the alarm in the hall has been fine for years. He may even be right that it only chirps when the battery is low. But a smoke alarm is a small, cheap thing that protects the whole house, and replacing one is a job you can finish in an afternoon with a stepladder, a screwdriver, and the box the new one came in.
Local option: New Plan Care gives families in the St. Louis area in-home help so a parent can stay home: companionship, help with bathing and dressing, meals, and overnight care. Call (314) 405-0887.
Before you climb
Look at the back of the old unit. Most alarms print a manufacturer date and a replacement guideline on the back or the side. Follow the printed label or the manual, not a number you half remember from a neighbor. Then notice how the old one is powered. Some run on a replaceable battery, some on a sealed battery that is not meant to be swapped, and some are wired into the house's electrical system. A wired unit is a job for an electrician, not a stepladder, so stop here and call one if that is what you find.
Buy the same kind of alarm, or the kind the packaging says suits the rooms where it will go. Some types respond faster to smoldering fires and some to flaming ones, and many homes do best with a mix. Read the box rather than trusting the shelf label.
The order that works
Switch the old alarm off at its button or remove its battery first. Unscrew it from the ceiling or wall. If the new unit uses the same mounting plate, keep the plate and screw the new unit onto it. If it does not, mount the plate where the instructions show, keeping the screws in the ceiling joists or wall studs rather than just the drywall.
Place the new alarm away from the kitchen and bathroom, where steam and cooking smoke set off false alarms, and away from the corners of rooms, where the air moves poorly. Snap it onto the plate, insert the battery if it needs one, and press the test button. Wait for the sound. Then press the hush button if the unit has one, so you know it responds to a press.
Mark it and hand it over
Put a small piece of tape on the new unit and write the word new on it, so the next person knows which one is which. Keep the box and the manual in the same drawer as the spare batteries. Then walk the rest of the house and check each alarm the same way, one at a time.
Let Dad stand at the top of the ladder and point at the spot where the new one should go. He will enjoy being right about the ceiling, and you will enjoy not having to argue about it.