Fire - Smoke and CO Detectors
Cost about $60 each. Cheapest to buy direct from Kiddie. Check Kiddie site for the latest model. Want hardwired AC, Smoke and CO, replaceable (ideally rechargeable) batteries.
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They have a timer inside that sounds an alarm after 7 or 10 years from first use. When it is end of life they need to be replaced.
Can buy in packs of three.
Use 18/4 security wire for smoke detectors. Buy 4 wires, and wire them properly. Note that by code, the wire for the smoke alarms must be red, specifically for fire signals and 18GA. Do not use other kind of wires, or you will risk failing the inspection. Smoke sensors are checked by both the wiring inspector and the fire marshal, and one of them will find it out.
Smoke detectors should be divided into zones, eg each house floor would be a zone. Need to wire for a smoke detector in every room. Smoke detectors can be in the ceiling soffits.