Whole-house detection set

Three interconnected photoelectric smoke alarms and one combination CO unit, pre-paired out of the box: any one detecting sounds all four, with a voice announcement naming the room. That is the configuration that actually wakes people on a different floor, and it is what the individual alarms on plates 3, 6 and 14 add up to for about fifteen per cent less.

Sealed ten-year batteries throughout, so all four reach end of life together. Covers a typical three-bedroom house: one per storey plus one outside the sleeping area.

Fitting and care. They arrive paired; do not factory-reset them unless you are adding units, and if you do, re-pair every unit rather than the new one only. Fit all four on the same day and record the date. Test the link monthly from a different unit each time so every radio gets exercised. Vacuum vents twice a year. If the house has a detached garage or an annex, check the link reaches before you fix anything to a ceiling — range is generous but masonry and foil-backed insulation both cut it.