another detector tip from my Fire/Rescue days:

write the month and yr on batteries when you replace them (no guessing how old)

use a sharpie pen to write the install date on the inner lid of dectectors (helps with the "when did I buy this" cogfog)

also put replace battery, etc on your calendar.We d ours when the time changes 2x year, which is laso when they are usually on sale in the hardware stores.