Firex · Hardwired smoke alarm
Firex i4618 / i4618AC: discontinued — what replaces it
Also printed as: i4618A, i4618AC
Quick answer
Firex is a brand Kidde took over; Kidde now lists the i4618AC as discontinued and points to its 20SAR hardwired alarm as the upgrade. Kidde's 20-9003 adapter names the i4618 family among the older plugs it can connect to a newer Kidde alarm, so the ceiling wiring can usually stay — confirm the exact pairing first.
Last checked
At a glance
- Status
- Kidde marks the Firex i4618AC as discontinued1
- Kidde's advice to Firex owners
- Kidde bought the maker of Firex alarms in 2009, says Firex products are no longer made or supported by their former maker, and advises replacing them with a current Kidde model2
- Sensor type
- Ionization1
- Power
- Wired to 120 V AC household power, with a 9 V backup battery1
- Backup battery
- The guide lists approved 9 V batteries (for example Energizer 522 or Duracell MN1604/MX1604) and says not to fit lithium batteries3
- Low-battery signal
- A chirp about every 30–40 seconds for at least seven days3
- When to replace
- NFPA says every smoke alarm must be replaced 10 years after its manufacturing date4
- Interconnect
- Up to 24 devices on one loop, 18 of which can trigger the rest (smoke, CO and heat alarms)1
- Older Kidde accessories
- The guide says this alarm does not work with Kidde CO relays and strobes made before November 1, 20113
- Warranty (as sold)
- Five-year limited for the i4618AC series3
Replacing it
- Replacement named by Kidde
- Kidde's i4618AC page offers the 20SAR (Smoke Alarm, Hardwired with AA Backup Battery) as the upgrade1
- About the 20SAR
- Hardwired, photoelectric sensor, two replaceable AA backup batteries, interconnects with other Kidde alarms5
- Keep the old wiring plug
- Kidde's 20-9003 adapter guide names i4618, i4618A and i4618AC among the older harnesses it can connect to a new Kidde alarm with the newer connector6
- Check the pairing first
- Kidde says to confirm both the old and the new model in the adapter's user guide or compatibility guide; if your ceiling plug doesn't match the ones shown, the new alarm's own harness has to be wired in instead6
- Mixing with Kidde alarms
- Kidde lists the Firex i4618 among models tested as interconnect-compatible with Kidde alarms2
- Recalls
- Search CPSC's recall list for your exact model before reusing or reselling an alarm7
Related models
Other models that cite the same adapter
Each link goes to another model page that cites the same adapter document. Whether two alarms can share a plug is answered in that document, on the model page.
Common questions
When should a Firex i4618 be replaced?
NFPA says every smoke alarm must be replaced 10 years after its manufacturing date4
What replaces the Firex i4618?
Kidde's i4618AC page offers the 20SAR (Smoke Alarm, Hardwired with AA Backup Battery) as the upgrade1
Which adapter guide lists the Firex i4618?
Kidde's 20-9003 adapter guide names i4618, i4618A and i4618AC among the older harnesses it can connect to a new Kidde alarm with the newer connector6
Sources
- Kidde — Firex Hardwired Smoke Alarm i4618AC (product page) checked 2026-10-31
- Kidde — What Other Products Will Kidde Alarms Interconnect With? checked 2026-10-31
- Kidde — Smoke Alarm User Guide, i4618AC / i4718AC / i5000AC Series (PDF) checked 2026-10-31
- NFPA — Smoke Alarm Information checked 2026-10-31
- Kidde — Smoke Alarm, Hardwired with AA Backup Battery 20SAR (product page) checked 2026-10-31
- Kidde — 20-9003 Wiring Adapter User Guide (PDF) checked 2026-10-31
- CPSC — Recalls & Product Safety Warnings checked 2026-10-31
Facts are restated in our own words. If a source page changes, the "checked" date tells you how fresh our reading is. Spot something out of date? Open an issue on GitHub.
Published October 31, 2026. Part of the Firex brand hub.