Shelly GAS (CNG)

Length x Width x Height

- Length: the longest side of the device

- Width: the shorter side of the device

- Height: the vertical dimension of the device

The physical weight of the device, typically measured in grams (g) or ounces (oz).

Weight can be important for installation considerations, especially for wall-mounted or battery-powered devices.

Powered by direct electrical connection to your home's power supply, either as a plug-in unit or through a fixed mains connection.

Combustible gas sensors draw far more current than a motion or door sensor, so almost every fixed gas detector runs on mains power and stops working during a blackout unless it has a battery backup.

Battery-powered devices typically use standard batteries like AA, AAA, or button-cell batteries (CR2032, CR123A), which are easy to replace and widely available.

A gas detector that runs on batteries alone is rare, and the ones that exist trade sensitivity or sampling frequency for battery life.

How long the device runs before the batteries have to be replaced or recharged.

On a mains-powered detector this figure usually refers to the backup battery, which only has to survive a power cut, not years of continuous sensing.

A built-in or replaceable battery that keeps the detector sensing when mains power fails.

Gas leaks and power cuts often happen together, for example when a storm knocks out the supply or when someone trips a breaker while working on an appliance. A detector without backup power is simply off during those hours.

Range: The 2.4 GHz band offers a longer range, meaning it can cover larger areas and penetrate solid objects like walls more effectively than 5 GHz.

Speed: Generally, 2.4 GHz provides slower speeds compared to 5 GHz due to a lower maximum data rate.

Interference: More prone to interference since many other devices (like cordless phones, microwaves, and Bluetooth devices) operate on the 2.4 GHz frequency, leading to potential congestion and slower network performance.

A WiFi gas detector needs no hub, which makes it the simplest option for a single kitchen or boiler room.

Range: Offers a shorter range compared to 2.4 GHz and may have difficulty penetrating walls and other obstacles.

Speed: Typically provides faster speeds and higher data rates due to more available bandwidth.

Interference: Less prone to interference as fewer devices operate on this frequency, leading to a more stable connection.

Bluetooth is a wireless communication technology used for exchanging data over short distances.

On gas detectors, Bluetooth is usually there for setup and pairing rather than for day to day alerts, since the alarm has to reach you when you are out of the house.

Z-Wave is known for its low power consumption, making it ideal for battery-powered devices. It supports a mesh networking topology, allowing devices to communicate with each other directly or through intermediary nodes, thus extending the overall network range and enhancing reliability. The protocol supports data rates of up to 100 kbps, suitable for transmitting control commands and sensor data.

Zigbee is a wireless communication protocol designed for low-power, short-range applications, commonly used in smart home devices, industrial automation, and other areas requiring reliable, low-data rate communication. It features low power consumption, making it ideal for battery-operated devices, and supports short-range communication, typically up to 100 meters. Zigbee employs mesh networking, allowing devices to relay data through each other to extend range and improve reliability. It supports data rates up to 250 kbps, suitable for small data packets, and ensures interoperability among devices from different manufacturers if they conform to Zigbee standards. Security is robust, with AES-128 encryption for data protection.

Zigbee devices need a Zigbee-compatible hub to connect and communicate with other devices in your smart home setup.

Because a gas detector is mains powered, it usually acts as a Zigbee router as well, strengthening the mesh for the battery sensors around it.

Thread is a wireless communication protocol designed specifically for Internet of Things (IoT) devices, providing secure, reliable, and scalable networking. Unlike some other protocols, Thread is IP-based, which means it can seamlessly integrate with existing internet infrastructure. It operates in the 2.4 GHz frequency band and uses mesh networking to enhance reliability and extend range by allowing devices to relay data through each other.

Thread is optimized for low power consumption, making it suitable for battery-operated devices. It supports low-latency communication, which is crucial for real-time applications like home automation and security systems. The protocol ensures high security with AES-128 encryption and end-to-end security at the network layer. Thread also supports over-the-air updates, ensuring devices can stay up to date with the latest features and security patches.

Thread-enabled devices require a Thread Border Router (such as certain smart home hubs or routers) to connect to your home network and other Thread devices.

Additional connectivity options not covered by the standard protocols.

This may include proprietary sub-GHz radios, RF interconnect links between alarms, or a wired relay output.

Google Home serves as a central hub for a variety of smart devices, including lights, thermostats, cameras, and speakers. It leverages Google Assistant for voice control, enabling users to manage their smart home with simple commands.

Amazon Alexa is one of the most widely used smart home systems, known for its compatibility with a vast array of devices. Users can control everything from smart lights to appliances using voice commands through Echo devices.

Apple HomeKit is designed for users in the Apple ecosystem, providing a seamless way to control compatible smart devices through iOS devices using the Home app or Siri. It emphasizes security and user privacy.

HomeKit exposes gas detectors as a leak or smoke style sensor, so a leak can raise a Critical Alert that ignores Do Not Disturb on your iPhone.

SmartThings is a flexible platform that connects a wide range of devices from different brands, offering a unified interface for control. It supports various communication protocols, allowing for extensive device compatibility.

Home Assistant is an open-source platform that allows for extensive customization and integration of a wide variety of smart devices. It supports a multitude of protocols and brands, making it ideal for tech-savvy users.

Local control matters more here than in most categories: a gas alarm that only reaches you through a manufacturer cloud goes silent the moment that cloud or your internet connection does.

IFTTT (If This Then That) is a web-based service that allows users to create simple automation sequences, known as applets, which enable different devices, services, and applications to work together seamlessly. It connects a wide range of products and services, facilitating interoperability and enhancing functionality.

Matter is a unified, open-source connectivity protocol designed to standardize and simplify communication between smart home devices from different manufacturers. Developed by the Connectivity Standards Alliance (formerly the Zigbee Alliance), Matter aims to improve interoperability, security, and reliability across various smart home ecosystems.

Matter operates over existing networking technologies, including Ethernet, Wi-Fi, and Thread, providing flexibility in device connectivity. Its IP-based nature allows seamless integration with existing internet infrastructure and cloud services. Matter uses a mesh networking topology, particularly when operating over Thread, to enhance range and reliability by allowing devices to relay data through each other.

Security is a cornerstone of Matter, with end-to-end encryption and secure device onboarding processes ensuring robust protection for data and privacy. Matter also supports over-the-air updates, allowing devices to stay current with the latest features and security enhancements.

Detection of natural gas, whose main component is methane (CH4). It is also sold as CNG, and it is what reaches most homes through a pipeline.

Methane is lighter than air, so a natural gas detector belongs high on the wall or on the ceiling, within a few metres of the boiler, cooker or gas meter.

Detection of liquefied petroleum gas: propane, butane and the bottled mixtures used for cooking, heating, caravans and boats.

LPG is heavier than air and pools at floor level, so these detectors are mounted low, roughly 30 cm above the ground. A unit calibrated for methane will not reliably catch a propane leak, which is why several brands sell the same housing in two versions.

Detection of carbon monoxide (CO), the odourless gas produced when a fuel burns without enough oxygen.

CO and combustible gas are different hazards that need different sensors: one warns that gas is escaping unburnt, the other that it is burning badly. Combination units cover both from a single device, but a dedicated CO alarm is usually placed differently, closer to sleeping areas.

The sensing technology used to measure gas concentration.

- Semiconductor (MOS): cheap and sensitive, the most common choice in smart detectors, but more prone to drift and to false alarms from cooking fumes, alcohol or aerosols.

- Catalytic bead: burns the gas on a heated element and reads the heat produced. Stable and linear across the explosive range, which is why it dominates certified combustible gas alarms.

- Electrochemical: the standard for carbon monoxide, accurate at low concentrations and low power, but not used for methane or propane.

- Infrared (NDIR): no chemical reaction and no drift, mostly found in industrial equipment rather than household units.

The gas concentration at which the detector sounds the alarm, normally given as a percentage of the Lower Explosive Limit (LEL).

The LEL is the concentration at which a gas becomes flammable, so an alarm set at 6% LEL fires at roughly one sixteenth of a dangerous mixture. European standard EN 50194 requires the alarm below 20% LEL; most home detectors are set between 5% and 10% LEL. A lower threshold gives you more time, at the cost of more nuisance alarms.

Some detectors report the reading in ppm instead, which is the usual scale for carbon monoxide.

The detector reports the measured gas concentration as a number, in the app or on the device itself, instead of only switching between normal and alarm.

A live reading tells you whether a value is climbing slowly (a small leak on a fitting) or spiked once (a burner that failed to light), and it lets you build automations that react before the alarm threshold is reached.

How long the gas sensing element stays within specification before the whole unit has to be replaced.

Gas sensors age whether or not they ever see gas. Five years is typical for combustible gas cells and seven to ten for good carbon monoxide cells, and a detector kept past that date can read low without any visible sign of failure.

Push notifications sent to your phone when the detector goes into alarm.

This is the whole point of a connected gas detector: a local siren only helps if somebody is at home to hear it, while a push notification reaches you at work and lets you call a neighbour or the gas company.

The loudness of the built-in sounder, measured in decibels at one metre.

Household gas detectors run from about 70 dB, which is audible in the same room, to 85 dB, which carries through a closed kitchen door and is the level required by most smoke and CO standards.

The detector announces what is wrong with a spoken message instead of only beeping.

A voice prompt separates a real gas alarm from a low battery chirp or a sensor fault, which matters at three in the morning when a pattern of beeps means nothing to anyone.

A warning when the battery, or the backup battery, is running out.

Ideally the warning arrives in the app as well as through the local chirp, so it does not go unnoticed in a garage or a boiler room nobody enters for weeks.

A distinct signal when the device itself has a problem: a failed or aged sensor, an interrupted self-test, or a lost connection to the hub.

A gas detector fails silently by design, since a dead sensor simply never alarms. Fault reporting is what turns that silent failure into something you can act on.

The detector can close the gas supply when it alarms, either through a dedicated output for a valve manipulator or by triggering a compatible smart gas valve in the same app.

This is the difference between being told about a leak and having it stopped. It matters most when the house is empty, and it is the main reason to prefer a detector that belongs to an ecosystem with a matching valve actuator.

A screen on the device that shows the current gas level or the device status without opening the app.

Useful during installation and when checking a suspected leak by hand, and the only readout available if the network is down.

The detector checks its own sensor and electronics automatically, on a schedule, and reports the result.

Unlike a smoke alarm, you cannot test a gas detector by holding something under it, so an automatic self-check is the practical way to know the unit is still alive.

The ability to silence the sounder for a period, from the button on the device or from the app.

Once you have ventilated the room and closed the tap, the alarm often keeps sounding while the sensor clears. Being able to mute it, remotely included, is what keeps people from unplugging the detector and forgetting to plug it back in.

Several detectors sound together: when one alarms, the rest of the group alarms too.

In a house where the boiler is in the basement and the bedrooms are two floors up, interconnection is what makes a leak audible where people actually sleep. Smart detectors usually do it by grouping units in the app rather than by wiring them together.

The safety standards the detector has been tested against, such as UL 1484 in North America, EN 50194 in Europe for combustible gases, or UL 2034 and EN 50291 for carbon monoxide.

Certification is what separates a tested life safety device from a sensor module in a plastic case. Look for the standard and the certifying body, not only a CE mark, which for these products is often self-declared.

The ability to create automated actions based on sensor readings or schedules.

A gas alarm is a good trigger for more than a notification: closing the valve, switching on the extractor fan, unlocking the door, turning on the lights on the way out.

The ability to track and store historical data over time.

A log of past alarms and readings is what tells you whether a detector has been reacting to a slow leak on a fitting or to the same burner failing to light every morning.