Tips

A few times a year, use a vacuum cleaner (hand-held or full-sized with extension tube) to gently remove dust from the slots cut into the unit's cover. Dust in those slots could slow the entry of smoke and interfere with early detection of a fire.
Never decorate any part of a smoke alarm (including the outer cover) with paint, stickers, hanging objects, etc. This can impair function.
Smoke detectors have a reliable service life of ten years. After ten years, replace the smoke detector with a new one.
If you move into a home with existing smoke detectors of an unknown age, look at the manufacturer's label on the back of the device. It might display a date of manufacture and you can use that date to calculate the device's age. If you cannot find a date of manufacture, replace the unit with a new one as soon as possible.
Wear ear protection when you test the smoke alarm. It's very loud and you will be right next to it when you're testing it.