How Does Your Carbon Monoxide Alarm Work?

For homeowners across the UK, safety goes beyond fire detection; it must include guarding against the 'Silent Killer'—Carbon Monoxide (CO). Understanding how your CO alarm functions is not just about curiosity—it’s about ensuring compliance and achieving true peace of mind.

This article breaks down the science behind the technology, clarifies what UK law demands, and explains why a reliable CO alarm is non-negotiable this heating season.

1. The Silent Threat: Understanding Carbon Monoxide (CO)

Carbon Monoxide is a colourless, odourless, and tasteless toxic gas produced by the incomplete burning of carbon-containing fuels (gas, oil, wood, charcoal, etc.). Common sources in a UK home include:

• Boilers and Central Heating Systems

• Gas Fires and Cookers

• Solid Fuel Appliances (Log Burners, Open Fires)

• Blocked or cracked chimneys/flues

Because CO is undetectable by human senses, a dedicated electronic alarm is the only reliable safeguard.

2. The Science Behind the Safety: How CO Alarms Detect the Gas

The vast majority of modern, certified CO alarms—including those compliant with the necessary EN 50291 standard—utilise a sophisticated electrochemical sensor.

The Electrochemical Sensor Explained:

The sensor relies on a small chemical cell, typically an acid-electrolyte layer sandwiched between two electrodes.

1. Gas Entry: When CO gas enters the alarm casing, it diffuses through a semi-permeable membrane and reaches the chemical cell.

2. Chemical Reaction: The CO gas reacts with the electrolyte, which generates a small electrical current.

3. Signal Generation: The intensity of this electrical current is directly proportional to the concentration of CO gas present in the air.

4. Microprocessor Analysis: A built-in microprocessor continuously monitors this current. If the current crosses a predetermined threshold for a specified period (see Section 3), the alarm is triggered.

Technical Note: Unlike smoke alarms (which often use photocells), CO alarms do not immediately sound off at low concentrations. They are designed to measure concentration (parts per million, ppm) over time. This prevents nuisance alarms while ensuring rapid warning for dangerous build-ups.

3. UK Standards: What EN 50291 Requires

For UK consumers focused on compliance and safety, the EN 50291 standard is crucial. This standard dictates the response times based on CO concentration.

Crucially: All reputable CO alarms sold in the UK must display this standard. If an alarm only sounds at high levels (e.g., above 300 ppm) but doesn't track time, it does not meet the necessary safety criteria for UK homes.

4. Installation and Placement Compliance

For maximum effectiveness, alarms must be correctly sited according to manufacturer instructions and best practice:

• In every room containing a fuel-burning appliance.

• On the ceiling or wall (depending on manufacturer guidance), near the appliance.

• At breathing height in rooms often slept in.

• Not near windows, vents, or in dead air spaces.

📣 Secure Your Home with Wisualarm CO Detection

Don't compromise on the safety of your family or your compliance obligations. The Wisualarm Carbon Monoxide Alarm is engineered specifically for the demands of the UK market:

• Certified Protection: Fully tested and compliant with the essential EN 50291 standard.

• 10-Year Electrochemical Sensor: Utilises a high-quality, long-life sensor for reliable, decade-long monitoring.

• Maintenance-Free: Features a sealed 10-year battery, eliminating the hassle and risk of annual battery changes.

• Digital Display: Provides real-time ppm readings, giving you immediate insight into your home’s air quality.