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Smoke and Carbon Monoxide Detector Alarms


Carbon monoxide (CO) is a colorless, odorless, and tasteless gas that is slightly less dense than air. Breathing it in, can make you sick and unwell, and will kill you when exposed to high levels. It disrupts the action of of your blood’s ability to carry oxgen, thereby causing the death of cells, and eventually can cause death.

In correctly burning fuel appliances  such as gas boilers, oil boilers or solid fuel boilers, carbon monoxodide levels are well below any actionable levels. In an appliance that has not been maintained or working according to manufacturers instructions, carbon monoxide levels can start rising and be pumped into areas in which people live or sleep.

It is in areas of high risk, or near fuel burning appliances, where carbon monoxide detectors can potentially save lives and prevent long term health complications due to prolonged levels of exposure. A standalone or combined detector can be a very small price to pay in order to save lives.

Smoke and Carbon Monoxide Detector Alarms.

It is a part of building regulations that certain measures are required under certain circumstances. For example, when you are letting out a property on rent, smoke alarms are required on all levels where there is a room that is used for living accomodation purposes. In addition, heat alarms may be required in the kitchen.

A carbon monoxide alarm is mandatory if there is a solid fuel burning appliance in the room which is used wholly or partly as a living accomodation. In other cases carbon monoxide alarm detectors may be required by certain organisations when open flued gas appliances are present, that is however not mandatory in uk, although this may change.

Scotland has different rules regarding this, in that rented properties with any type combustion appliance requires a carbon monoxide alarm detector 1-3 meters from the appliance. It should not be place in a dead zone, that is within 300mm from the ceiling edges.


Intelligent and Smart Carbon Monoxide Detector Alarms

Since the last couple of years, there has been an increase in Smart connected Detectors. Companies such as Nest have completely changed the design of Smoke and Carbon Monoxide alarms or detectors. They come with a raft of features as simple as voice, ranging to additional guided lights and auto testing.

Even some of these products such as the Nest Protect, link up with your Smart Nest Thermostat, and shut the appliance down in the event carbon monoxide or smoke is detected. These alarms tend to have very sophisticated modern sensors, with the ability to distuingish between steam or smoke.

Carbon Monoxide Detector Alarm Placement

carbon monoxide detector position placement image
carbon monoxide detector position placement image


The detector should be, placed in every room with a fuel burning appliance. As stated in local laws and regulations, it is mandatory when certain types of fuel burning appliances are present, such as solid fuel appliances or solid fuel boilers. It is also generally highly recommended where open flued appliances such as Open Flue boilers are present.

  • It is recommended to be placed a minimum of 1m upto a maximum of 3m away from the appliance.
  • Avoid dead spaces, ie 300mm horizontally from the ceiling edge and 100mm vertically from the wall edge
  • Mains powered detectors should adhere to electrical standards also. Search for prescribed electrical zones.
  • Should have a clear path from appliance to the detector ie not placed inside a cupboard etc.
  • Alarm should be tested regularly and/or annually. Some detectors, as stated earlier can perform auto testing.


nest protect smoke and carbon monoxide detector placement
nest protect smoke and carbon monoxide detector placement


Some manufactures may have their own product specific placement guidelines. Example above shows the Nest Protect placement guidelines. Usually in this industry, manufacturer’s guideline will exceed or override general guidelines. Manufacturer’s guideline should always be followed. See the installation manual for your specific detector.


Shown below is a comparison of smoke and carbon monoxide detector alarms.

BrandModelUrlLowest priceSmoke / Carbon Monoxide COSensor Life / Unit LifeBatteries /Battery LifeKey Features
Kidde7COCProduct Page£13.18Carbon Monoxide CO10 year sensor3 x AAA Included-
Kidde7DCOProduct Page£18.64Carbon Monoxide CO10 year sensor3 x AAA IncludedLCD Screen
Kidde10SCOProduct Page£16.19Smoke and Carbon Monoxide CO10 year warranty9V battery (1-2 years)Voice
Kidde10LLDCOProduct Page£16.19Carbon MonoxideLCD Screen
KiddeCO-9DProduct Page£24.99Carbon Monoxide7 year warranty2 X 1.5 DC BatteryLCD Screen
HoneywellXC70Product Page£17.55Carbon Monoxide CO7 yearsBuiltin 7 year life-
HoneywellXC100Product Page£23.01Carbon Monoxide CO10 YearsBuiltin 10 year life-
HoneywellXC100DProduct Page£30.32Carbon Monoxide CO10 YearsBuiltin 10 year lifeLCD Display
FireangelCO-9BProduct Page£12.60Carbon Monoxide CO1 Year battery Included-
FireangelCO-9XProduct Page£15.70Carbon Monoxide CO7 yearsBuiltin 7 year life-
FireangelCO-9DProduct Page£21.50Carbon Monoxide CO7 yearsBuiltin 7 year lifeLCD Display
Nest ProtectProtect v2Product Page£89Smoke and Carbon Monoxide CO10 YearsMains / BatterySmart Device
Nest ProtectProtect v2Product Page£89Smoke and Carbon Monoxide CO10 YearsBatterySmart Device

The following table shows the exposure levels and it’s health effects.

CO Level ppmConditions and Health EffectsInstitute
0Normal, Fresh Air
9Maximum allowable short term exposureASHRAE
10-24Possible health effect with long-term exposure
25Max TWA exposure for 8 hour work dayACGIH
50Maximum permissible
100Slight headache after 1-2 hours
200Dizziness, nausea, fatigue, headache after 2-3 hours of exposure
400Headache and nausea after 1-2 hours exposure/life threatening in 3 hours
800Headache, nausea, and dizziness after 45 minutes / Collapse and unconsciousness after 1 hour of exposure, death with 2-3 hours
1600Headache, nausea, and dizziness after 20 minutes , death within 1-2 hours
3200Headache, nausea, and dizziness after 5-10 minutes , death within 1 hour
6400Death within 30 minutes
12800Death within 1-3 minutes of exposure


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