The updated Kidde Firex KF20 and KF20R alarms are mains powered, interlinking optical smoke alarms that use up to 70% less energy than previous Firex models. The KF20 has an alkaline battery back-up and the KF20R, a self-charging lithium battery back-up. The units are hard wired and can be interlinked with other units from the series to create all round fire protection within the home.
Please note: The Kidde Firex KF20 (previously KF2 / 4973 / PADC240) and KF20R (previously KF2R / 4985 / PAR230) are replacements for the Kidde 223/9HI and 223/9HILL series, and can be electrically interlinked. However, the new models cannot be used on the old base plates for the 223/9HI and 223/9HILL series as they use different style connector blocks. This means that base plates must be swapped over on those stated models and connectors need to be replaced.
All of our product reviews are written by real customers that have purchased this product from us and are published without modification.
I M
13th July 2026
C H
Replacement for existing system very easy to install comes with the back up batteries
(Duracell) very pleased 😀
10th July 2026
S R
Easy direct replacement for previous product. Didn’t need to replace the base. Very prompt delivery. Thank you
22nd June 2026
| Product Code | KEKF20 |
|---|---|
| Brand | Kidde |
| Manufacturer's Part Number | KF20 |
| Approvals & Markings | CE Marked |
| Back-Up Battery Type | Alkaline |
| British Standard Grade | Grade D2: Mains Powered (replaceable backup) |
| Colour | White |
| Compliance | BS 5839-6 |
| BS EN 14604: 2005 | |
| Connection | Wired |
| Display | LED Indicators |
| Fixing Options | Screws (included) |
| Installation Position | Ceiling |
| Local Legislation | Scottish Legislation (2022) |
| Welsh Legislation (2022) | |
| 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) |
|
| Weight | 280g |
| Datasheets |
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 |
Direct replacement for older firex model, as suggested by safelincs. Easy fit replacement, good price and fast delivery.