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Mains Powered Smoke Alarms & Heat Alarms with Alkaline Back-up Battery - Kidde Firex KF Series

Front view of kidde firex mains powered optical smoke alarm alkaline battery backup in white with sensor and vent details
4.8 out of 5 stars

20+ In Stock

Estimated dispatch: Monday 15th June
Qty: 1

£20.80 inc VAT

£17.33 ex VAT

Qty: 2

£20.50 inc VAT

£17.08 ex VAT

Qty: 5

£19.90 inc VAT

£16.58 ex VAT

Standard Delivery

Will usually be delivered in 2-3 working days

£4.20 inc VAT

Next Day Delivery

Will usually be delivered the next working day

£7.00 inc VAT

The updated Kidde Firex range of smoke and heat alarms are mains powered, interlinking units that now use up to 70% less energy than previous Firex models. Hard-wired with alkaline back-up batteries, these alarms can be interlinked with other units from the series to create all round fire protection within the home; when one alarm detects smoke/heat and sounds, all units will sound. Installing the right sensor types in your property gives you the fastest possible response time with the minimum number of false alarms.

  • Mains powered with alkaline back-up battery
  • Suitable for installations complying to
  • Kitemarked to and CE marked
  • 6 year warranty
  • Please see our replacement for the KF10 Ionisation model which has been discontinued
  • A maximum of 24 units can be interlinked via signal cable
  • Neat slimline design
  • 230V hard-wired smoke alarm
  • Up 70% less energy consumption compared to previous Firex models
  • LED display
  • Test/Hush button
  • Low battery warning chirp - can be silenced for 8 hours
  • Supplied with dust cover (to protect unit temporarily if you carry out dusty work)
  • Dimensions (HxDia.): 38 x 133mm
  • This alarm is also suitable for both the Welsh and Scottish updated 2022 legislation

Please Note: The Kidde KF Firex models are replacements for the older Firex 4000 series, Kidde 9HI and Kidde 9HILLs and can be interlinked, however the new models cannot be used on the same base plates and use different connector blocks.

Customer Reviews

Customer Reviews (130)

4.8 out of 5 stars

Reviews by Real Customers

All of our product reviews are written by real customers that have purchased this product from us and are published without modification.

Rating: 5 / 5

Reviewed by

P R

Published on

26th April 2026

Direct replacement for a much older smoke alarm - plug n play. Very happy.

Applies to option(s): KF20 Optical Smoke Alarm

Rating: 4 / 5

Reviewed by

D M

Published on

23rd April 2026

It does the job

Applies to option(s): KF20 Optical Smoke Alarm

Rating: 5 / 5

Reviewed by

I E

Published on

4th October 2025

Safelincs gave excellent support in finding this replacement for a missing alarm

Applies to option(s): KF20 Optical Smoke Alarm

Rating: 4 / 5

Reviewed by

D B

Published on

26th July 2025

Easy to fit. No issues so far.

Applies to option(s): KF20 Optical Smoke Alarm

Rating: 5 / 5

Reviewed by

S N

Published on

4th July 2025

Good product with prompt delivery

Applies to option(s): KF20 Optical Smoke Alarm

FAQs

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Technical Data

Technical Data

Product Code KEKF20
Brand Kidde
Back-Up Battery Type Alkaline
British Standard Grade Grade D2: Mains Powered (replaceable backup)
Colour White
Local Legislation Scottish Legislation (2022)
Welsh Legislation (2022)
Approvals & Markings CE Marked
Compliance BS 5839-6
BS EN 14604: 2005
Connection Wired
Display LED Indicators
Fixing Options Screws (included)
Installation Position Ceiling
Material Plastic
Maximum Number of Linked Devices 24 Devices
Operating Temperature 0°C To +40°C
Positioning Bedrooms
Hallways
Living Rooms
Power Type Mains Powered (230V)
Product Range Kidde Firex
Recyclable Yes - Valpak's WEEE Distributor Take-back Scheme
Relative Humidity Up To 93%
Sensor Type Optical
Sound Level 85dB
Suitability Home
Warning Type Audible - Alarm Sounder
Warranty 6 Years
Dimensions (Unit)
  • Height: 39mm
  • Diameter: 133mm
Weight 280g
Datasheets
Interlink

Interlink

Alarms from the Same Series

The table below shows all the units that can interlink with the Firex KF Series.

Model Number Type of Unit Type of Interlink
KF10 Ionisation Smoke Alarm Hardwire interlink
KF10R Ionisation Smoke Alarm with Rechargeable Lithium Cell Hardwire interlink
KF20 Optical Smoke Alarm Hardwire interlink
KF20R Optical Smoke Alarm with Rechargeable Lithium Cell Hardwire interlink
KF30 Heat Alarm Hardwire interlink
KF30R Heat Alarm with Rechargeable Lithium Cell Hardwire interlink
KF1 Ionisation Smoke Alarm Hardwire interlink
KF1R Ionisation Smoke Alarm with Rechargeable Lithium Cell Hardwire interlink
KF2 Optical Smoke Alarm Hardwire interlink
KF2R Optical Smoke Alarm with Rechargeable Lithium Cell Hardwire interlink
KF3 Heat Alarm Hardwire interlink
KF3R Heat Alarm with Rechargeable Lithium Cell Hardwire interlink

Carbon Monoxide Alarms

Model Number Type of Unit Type of Interlink
4MCO CO Detector with Rechargeable Lithium Cell Hardwire interlink
K4MCO CO Detector with Rechargeable Lithium Cell Hardwire interlink

Compatible Alarms

Model Number Type of Unit Type of Interlink
1239HI Ionisation Smoke Alarm with Alkaline Battery Hardwire interlink
1239HILL Ionisation Smoke Alarm with Lithium Battery Hardwire interlink
2239HI Optical Smoke Alarm with Alkaline Battery Hardwire interlink
2239HILL Optical Smoke Alarm with Lithium Battery Hardwire interlink
3239HI Heat Alarm with Alkaline Battery Hardwire interlink
3239HILL Heat Alarm with Lithium Battery Hardwire interlink
4870 Ionisation Smoke Alarm with Alkaline Battery Hardwire interlink
4881 Ionisation Smoke Alarm with Lithium Battery Hardwire interlink
4973 Optical Smoke Alarm with Alkaline Battery Hardwire interlink
4985 Optical Smoke Alarm with Lithium Battery Hardwire interlink
4899 Heat Alarm with Alkaline Battery Hardwire interlink
4892 Heat Alarm with Lithium Battery Hardwire interlink
I240C Ionisation Smoke Alarm with Alkaline Battery Hardwire interlink
PADC240 Optical Smoke Alarm with Alkaline Battery Hardwire interlink