Interconnected smoke alarm, wireless

A smoke alarm in the basement is inaudible from an upstairs bedroom with the door closed, which is the exact condition it exists for. Interconnection solves it: when one unit detects, every unit in the house sounds, and voice announcement tells you which room it came from.

Wireless interlink pairs up to 18 units with no wiring. Photoelectric sensing, sealed ten-year battery. Buy at least one per storey plus one outside each sleeping area; they are cheaper together in the whole-house set on plate 24.

Fitting and care. Pair every unit before any of them go on a ceiling — it takes two minutes on a table and considerably longer up a ladder. Test the link, not just the unit: press and hold on one and confirm every other one sounds, and do that monthly. Keep at least one unit within radio range of each of the others; a long single-storey house or a detached garage may need an intermediate unit as a relay. Vacuum the vents twice a year and never paint any of them.