Interlinked alarm two-pack

One interlinked alarm is just an alarm. Two is the smallest configuration that does the thing interlinking exists for: a unit downstairs sounding the unit outside the bedroom, through a closed door, at four in the morning.

Pre-paired out of the box, photoelectric sensing, sealed ten-year batteries, voice announcement of the room. Expandable to eighteen units on the same link, so this is a sensible way to start a house and add to it a floor at a time.

Fitting and care. Pair on a table, fit on the same day, write the date on both. Put one where the fire is most likely to start and one where the people are, which usually means kitchen or basement, and the landing outside the bedrooms. Test the link monthly from each unit alternately. If you later add units, re-pair the whole group rather than adding to it, and re-test. Vacuum vents twice yearly and never paint either one.