A woman sits on a bed; lamp, mug, and FA3820X4 device are on the bedside table.
The FA3820X4 carbon monoxide alarm sits on a wooden worktop in a modern white kitchen.
Top and side views of FA3820X4, an oval device, 125mm x 67mm x 33mm technical drawing.
Instructional graphic: how to activate and test an FA3820X4 alarm in three steps.
Which? Best Buy August 2025 badge for CO alarm on green background.
FA3820X4 white fire alarm includes screws and an easy-to-install integrated mounting bracket.
Exploded view of FA3820X4 smoke alarm with tamper-proof, 10-year internal battery.
Close-up of FA3820X4 showing a TEST button and quiet self-test mode notification.
Exploded view of FA3820X4 smoke alarm with internal components and certification text below.
Close-up of the FA3820X4 alarm displaying a rapid carbon monoxide detection alert.
FA3820X4 carbon monoxide alarm with yellow warning light and ventilation instructions below.
Close-up of FA3820X4 carbon monoxide alarm with red light showing previous activation.
Close-up of the FA3820X4 alarm showing its sleep-easy function and battery warning.
Close-up of FireAngel FA3820X4 CO alarm featuring red warning light and silence button.
FA3820X4 alarm installation guide shows shelf/wall mounting steps and required tools.
Light grey FA3820X4 sofa with round cushion and blanket, under a speaker on a green wall.

FA3820X4

Carbon Monoxide Alarm, 10 Year Life-Time Battery

CO 5 Year Warranty Sealed battery Battery Silence

Product description

Looking for a CO-9X alarm replacement? With the latest sensing technology and a clear loud alarm, the FA3820X4 offers the highest level of CO detection for your home and replaces end-of-life CO-9X alarms.

Intelligent CO sensing technology enables the alarm’s high sensitivity mode to be activated if it predicts CO levels will increase to or above 180ppm for a quicker alert.

  • Advanced electrochemical sensor detects and provides a warning to low levels of carbon monoxide, and will provide a ventilate alert as this increases
  • Press the test button once for a complete alarm test with a quieter audible alert or press twice for a complete test with full alert
  • Pressing the large test button in the event of a low battery warning will activate the sleep easy feature which silences the low battery chirp for 8 hours
  • A 10 year battery is sealed within the alarm which will offer protection for the lifetime of the device, without needing to change the batteries
  • Suitable for homes in England, Wales and Scotland (under new guidance)
  • FireAngel alarms are rigorously tested to ensure unrivalled quality and longevity and come with a 5 year manufacturer’s warranty for peace of mind
  • Rigorously tested in-house and third party approved and certified to Kitemark standards
MoreLess

Looking for a CO-9X alarm replacement? With the latest sensing technology and a clear loud alarm, the FA3820X4 offers the highest level of CO detection for your home and replaces end-of-life CO-9X alarms.

Intelligent CO sensing technology enables the alarm’s high sensitivity mode to be activated if it predicts CO levels will increase to or above 180ppm for a quicker alert.

Installation & setup

Get the help and support you need to easily set up and install your FireAngel alarm for instant protection.

Installation guide

Installation guide

Click the icon to find out more about installing your pro connected app

Maintenance guide

Maintenance guide

Click the icon to find out how to maintain and test your alarm

Resources

To ensure you install the right alarm for your home, and one that's compliant with your local fire regulations, review our manual and data sheet or get in touch with our customer service team.

Product manual

Product manual

Click the icon to download the product manual

Datasheet

Datasheet

Click the icon to download the product datasheet

Related FAQs

Yes – this Carbon Monoxide Alarm is EN 50291-2 certified and IP44 splash resistant, suitable for all domestic settings, including caravan holiday homes, caravans, motor caravans, and boats.

See the installation instructions in the product box or product page for installation instructions.

From October 2022, the law changed surrounding carbon monoxide alarms in rented properties – for both the private and social sectors. As a private or social landlord, you will need to ensure you have a working carbon monoxide alarm 1‑3 metres away from any fuel burning appliances in a property (excluding gas cookers) and that any faults or repairs are carried out on the alarm in a timely manner.

Carbon Monoxide is produced when fuels burn incompletely – this could be from a boiler, gas fire, oven, log burner or a blocked flue or chimney. It can also travel through walls from adjoining properties, so as well as having an alarm next to appliances in your property we would also advise you to have one in living spaces and bedrooms. To help prevent a Carbon Monoxide leak we advise getting your appliances regularly serviced by reputable engineers who are gas safety registered.

See all faqs

Which? recommended for you

Trusted to protect you and your loved ones with our FA3322 Digital CO Alarm that is recommended by Which? the consumer champion.

which-fa3322
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Reviews from our customers

Five stars review

“I bought this as my old fixed unit had expired. The instructions are simple and it’s easy to use but a much more modern feel.”

Amazon Customer, Originally posted on amazon.com

Five stars review

“No need for battery replacements as it’s already sealed inside. Comes with 5 year warranty so what’s not to like.”

Amazon Customer, Originally posted on amazon.com

Five stars review

“Quality upgrade from my old detector. Great 10yr battery and was able to put it on a shelf instead of fixing to the wall,”

Amazon Customer, Originally posted on amazon.com

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Got a burning question? Get in touch

If you can't find what your looking for on our blogs and looking for further guidance and advice, our UK-based Customer Support team are on hand all week from 8:30am until 5:30pm, they can answer any further queries you may have on our products, solutions or services.