Hardwired smoke alarms — what your house is required to have

Establish what the house is required to have

The count and placement come from the code your jurisdiction has adopted, and are driven by the number of bedrooms and storeys rather than by square footage. Carbon monoxide alarm requirements sit alongside them and often apply where there is fuel-burning equipment or an attached garage. Adoption varies by state and city, so confirm locally rather than working from a national summary.

Watch for: A recommendation to add alarms everywhere without reference to what is actually required. Over-installing in the wrong locations — too close to a kitchen or a bathroom — produces nuisance alarms, and nuisance alarms are why people take batteries out.

Decide between hardwired, interconnected and wireless

Hardwired units take power from a circuit with battery backup, and are traditionally interconnected by an additional conductor between them. Wireless-interconnected alarms achieve the same all-sound behaviour by radio, which matters because running interconnect wiring through a finished house often means opening ceilings and walls.

Watch for: Mixing brands or models on one interconnected system. Interconnection compatibility is model-specific, and mismatched units frequently fail to trigger each other — the one thing the system exists to do.

The retrofit position in an existing home

Codes generally treat existing dwellings differently from new construction. Where alterations do not involve removing wall or ceiling finishes, alarms in existing homes are commonly permitted to be battery-powered rather than hardwired, and wireless interconnection is commonly accepted in place of an interconnect conductor. This is why a compliant retrofit is often far less invasive than people expect.

Watch for: A quote to open ceilings for interconnect wiring in a house where the retrofit allowance would apply. Ask the question explicitly before agreeing to the disruption.

Interconnect test and occupant handover

After power-up, verify that initiating one detector triggers the interconnected set as designed, and walk the household through hush, battery backup behaviour and replacement dates.

Watch for: A single unit that chirps or tests alone while the rest stay silent. Interconnect is the whole point of hardwired systems; a failed link is an incomplete job.

Document locations and replace-by dates

A simple map of detector locations, interconnect method and battery type is left with the household. Photoelectric versus ionization is less important than knowing what was installed and when it ages out.

Watch for: No record of what went in. The next service call should not start with a guessing game about which units are interconnected or expired.