Fire Detectors – Smoke Alarms

Fire Detectors - Smoke Alarms

Smoke detectors are devices designed to trigger an alarm when they sense smoke. Household smoke detectors, which are also known as smoke alarms, generally issue a visual alarm or an audible alarm when there is a fire. High tech commercial fire security devicesOpens in a new tab., on the other hand, are designed to send a signal to the control panel of the fire alarm connected to them. This, in turn, triggers the fire suppression system in the building, while sending a distress call to the local fire department.

Smoke detectors are housed in a disk-shaped plastic enclosure of about 150mm in diameter and 25mm thick, but the size and the shape of the device can vary. Smoke is detected by the device either by a physical process known as Ionization or optically. The sensitivity of smoke alarm makes them perfect for areas where smoking and burning are banned.

Unlike other fire protection devicesOpens in a new tab. that only have industrial application; smoke detectors can be used in residential, commercial and industrial structures alike. Residential smoke detectors ranges form interlinked main-powered unit to individual battery powered unit. If any of the units happens to detect smoke, they will trigger an alarm even if power in the building which is installed has gone out.  

Smoke alarms can cut in half the risk of dying in a home fire. The National Fire Protection Association reports 1.18 deaths per 100 homes without a fire alarm, while 0.53 deaths are recorded in a home with a working smoke alarm. Some possible reasons why some people still lose their lives in buildingsOpens in a new tab. where smoke detectors are installed when there is a fire could be that the alarm does not have working batteries or the alarm failed to detect the fire on time.  

In this article, we are going to be looking at the history of smoke detectors, the various types that are available, their working principle, and how to keep them in a great working condition.

History of smoke detectors

In 1890, the first electric automatic fire alarm was invented by Francis Robbins Upton, a close associate of Thomas Edison. The first European heat detector was patented by George Andrew Darby in 1902, in England.

Swiss physicist Walter Jaeger tried to invent a device that could detect poisonous gas. His expectation was that the poisonous gas entering the device would bind to ionized air molecules and alter current in a circuit in the device. Sadly, his device didn’t meet its purpose. A small concentration of the poisonous gas released had no effect on the sensory conductivity of the device.  Frustrated and Angry, Jaeger lit a cigarette and was shocked to see that a meter on his device had registered a noticeable drop in current. Smoke particles from the cigarette he lit have surprisingly done what the poisonous gas couldn’t. Jaeger’s experiment paved way for the development of modern smoke alarm.

In 1939, a special ionization chamber was devised by a Swiss physicist called Ernst Meili. The chamber was capable of detecting combustible gases.  He later went on to invent a cathode tube that could intensify the signal generated by the detection system to a level sufficient to trigger an alarm.

Ionization smoke detectors, is much cheaper today like this oneOpens in a new tab., were introduced to the US market in 1951. Back then, they were used in large industrial and commercial facilities. This was due to their large size and exorbitant price. Four years later (1955), simple residential fire detectors were developed. The USAEC granted the distribution of smoke detectors in 1963, but they were still very expensive.

In 1965, Duane D. Pearsall developed the first low-cost smoke detector for residential and domestic use. The detector, which was known as the “SmokeGard 700”, was easy to install and was powered by replaceable batteries. These units where mass produced in 1975. A couple of studies that were conducted in the early 1960s showed that smoke alarms responded faster than heat detectors.

The first single unit smoke detector was developed in 1970 and made available to the public the next year. It was a simple ionization smoke detector powered by a 9-volt battery. They were sold at $125.

Numerous technological developments took place between 1970 and 1976. One of these developments was the replacement of cathode tubes with solid state electronics, which made it possible to monitor the battery life of the device and to reduce its size. These detectors could also function with a very little amount of radioactive material. The smoke detector enclosure and the sensing chamber were modified for more efficient operation.  The rechargeable battery that was once used to power the device was replaced by a pair of AA batteries. In 1995, the 10-year lithium battery powered smoke detector was introduced to the US market.

Types of smoke detectors

Photoelectric smoke detector

Photoelectric detectorsOpens in a new tab. are detectors designed to use a light beam to detect smoke. Unlike ionization detectors that are effective for flaming fires, photoelectric or optical detector are better for alerting the occupants of a building of smouldering sources. For example, when a lit cigarette falls, the smouldering fire could engulf the area with dangerous gasses before a fire starts.

Ionization smoke detector

An ionization smoke detectorOpens in a new tab. uses electrically charged particles or ions to detect smoke in the air. According to the NFPA, ionization smoke detectors are more responsive to a flaming fire than an optical detector. A good example of a flaming fire would include a residential fire that startedOpens in a new tab. when a candle falls and ignites a couch or curtain.

Choosing between them

As you now know, both detectors can promptly notify the occupant of a building of a small fire before it spreads and causes serious damage. Since both of them have their highs and lows, it may be difficult for you to choose between them. To make an informed decision and choose the right one, you have to learn as much as you can about both of them.  To be on the safe side, you should follow the NFPA suggestionOpens in a new tab. to install both detectors in your home.

If you don’t know the type of smoke detector you have in your building, now is the time to check. See, you don’t need to be tech-savvy or have a solid technical background to check the detector in your home. All you got to do is to take a close look at the back of your detector for ionization or photoelectric. Once you have accurately figured out the type you own, promptly purchase the other type and install it next to your existing detector.  Alternatively, you can replace your present detector with a dual-sensor device, which combines both photoelectric and ionization technology in one unit.

Smoke alarm maintenance

As you probably now know, a working smoke detector can cut in half the chances of your dying in a fire.

The national fire fatality rate has been on the decline in the US. And this is because some states require smoke detectors to be installed in existing and new buildings. Presently, more than 80% of homes in the US have at least one smoke detector.

Unfortunately, the smoke detectors in many homes are either not working properly or aren’t installed in the right place. To ensure that your home is protected, install a smoke alarm on every floor of your building and near bedrooms-they have to be close to enough to wake you if a fire happens to break out during the night.

How to clean and test your smoke detector


Test your smoke alarm by pressing the test button until you hear the alert sound, then slowly release.


  • Carefully vacuum around the vents of your smoke alarms. This will reduce cobweb and dust-build up.  
  • Spray the surface of the smoke detector with insecticide to prevent insects from nesting inside the device. Be careful not to spray inside the detector.
  • Replace the 9 Volt batteries in your detectors each year.

When to replace your smoke alarm?

  • Smoke alarms are designed to last for 10 years.  After 10 years, their performance and efficiency begin to decline.  Also, the dust build-up, airborne contaminants, insects and corrosion of the circuits in the device may compromise its effectiveness.
  • Smoke alarms make a unique beep when it is faulty or when the battery in it needs to be replaced.
  • Do well to check the manufacturer’s instructions before changing the battery. Some smoke detectors on the market have a rechargeable battery. If you own this type of alarm, you may not be able to change the battery.
  • Smoke detectors with a user-replaceable battery may continue to beep even after you have changed the battery. The beep is likely an indication that the device is faulty and needs to be replaced.
  • Keep in mind that main powered smoke detectors may give a low battery beep after periods of extended power outage. You should be aware that the batteries in the device may need a couple of hours to recharge after the power is restored. It may take a longer time for the battery to be restored if the back-up battery was totally depleted. The rechargeable lithium batteries in your smoke detector may degrade quickly and ultimately becomes inoperable if there are too many periods of power outages over the life of the device.

Maintenance for leased and rented properties

If you are renting a property for some time, it will be required to maintain the smoke alarm installed in it and replace them when they are up to ten years.

Adhere to the following routine to ensure that your rented property is protected;

  • The smoke detector should be tested at least twice a year
  • Carefully check detector for a build of cobweb and dust
  • Vacuum around the smoke detector vent twice a year to remove dust that could affect the performance of the device
  • Check if the required power source is well connected and operating properly. Mains power smoke detectors usually have a light that indicates that they are properly connected.
  • Check if the detector is firmly secured in the right location
  • Spray insecticide around the device to prevent insects from nesting inside it.
  • Check if the detectors are within their service life, as some detectors need to be replaced every ten years. The replacement date is usually indicated on the device.
  • Replace batteries annually.

As time goes by, one or two of your smoke detector is likely going to go bad. When this happens, it is wise you employ the service of a licensed electrical contractor. Of course, you have the freedom to inspect and change your detector on your own, but it wise that you hire a trained electrician to do it for you.

Maintenance for tenants

  • Check if the green visual display light is on. This shows that the detectors are properly connected to a power source.
  • Test the alarm monthly by pressing the test button until you hear the alert tone.
  • Instruct your tenants not to tamper with the alarm or place any obstruction to restrict the air flow to the alarm.

Test your smoke detector

Smoke detectors are likely one of the most important safety items in your home that could promptly alert you and your loved ones of a fire before it spreads and goes out of control. These life-saving devices need to be tested periodically to ensure that they are working properly.

Why you should test your smoke detector

As you know, electrical devices are not designed to last forever. Batteries die and other parts of the device can wear out after a while. Replacing batteries and testing them regularly is an effective way to ensure the safety of your family and loved ones if there happen to be a fire in your home.

How often should you test your smoke detector?

According to the USFA, smoke detectors should be tested monthly and batteries should be replaced twice a year. Carefully read your smoke detector manual before testing it or replacing its battery. While smoke detectors ought to be inspected monthly, you may need to check them more often if any of the following apply;

  • If the device starts beeping without anyone touching it
  • If the smoke detector often gives false alarms
  • Heavy smoke from the kitchen triggers it regularly

According to the USFA, there are two major types of smoke alarms;

Hard wired

Like this oneOpens in a new tab. here, these detectors aren’t designed to be powered by 9-volt batteries, but by your home’s electrical system. But they usually have back-up batteries embedded in them so that they can remain operational in the event of a power outage. Just like battery powered detectors, hard-wired detectors need to be tested monthly to ensure that it is working properly.

Battery powered

Battery powered smoke alarms are designed to be powered by replaceable 9-volt batteries and are susceptible to defect. Monthly testing is important. Never put old or used batteries into your smoke alarm.

How to test your smoke detector

Since smoke detectors are not made exactly the same way, it is important that you check the manufacturer’s instruction for the right method to test it. Generally, the USFA states that most hardwired and battery powered detectors can be tested in the following ways;

  • Inform the members of the apartment that you are going to be testing the smoke alarms in your home. As you know, smoke detectors have ear-splitting alarms that could frighten little children. It is wise you tell members of the household of your decision to test the alarm so that anyone doesn’t get tensed up or scared.   
  • Ask a member of your family to go to the furthest point away from the smoke alarm in your home. This can help make sure that the alarm can be heard in every part of your home. Install an extra detector in areas where the alarm sound is faint or weak.
  • Gently press and hold the test button on your detector. It is likely going to take a couple of seconds for the alarm to start blaring. The device will continue to sound an alarm while the button is pressed.
  • Replace your batteries if the sound is non-existent or weak.  If has been six months since you changed the batteries in your detectors (Irrespective of the type you have in your home) replace them and test the new batteries one last time to ensure that they are working properly.
  • You should also inspect the vents of your detector to see if it blocked by dust or other substance that may prevent the device from functioning properly.

Don’t forget that smoke detectors have a life span of ten years. According to the USFA, smoke detectors should be replaced after ten years of usage.

Installing smoke detectors in your home is a great way to keep your family safe, but assuming they are working and not testing and cleaning them is a recipe for disaster. Take a couple of minutes to inspect them regularly can help ensure that they are in proper working condition.

Where to install your smoke detector in your home

Installing smoke detectors in a strategic part of your home will ensure quick or early detection of a small fire before it spiral out of control and cause large scale damage.

According to the NFPA, smoke detectors should be installed in several parts of the home. To ensure that you have enough smoke detectors, follow this checklist and install your alarm in these areas.

At stairways

This includes the top of the stairs leading to the second or the first floor and at the bottom of the staircase from the basement.

On every level of your apartment

This includes basements and garages and attics. Depending on how large your basement is, you may need to install one in each corner.


Detectors should be installed in every bedroom and hallways in the home.

Large rooms

Install at least one smoke alarm in your living room, but ensure that they are at least ten feet away from the kitchen, as this can trigger the detector.

Locations to avoid

To ensure the best performance of your smoke detectors, you have to avoid the following areas;

  • Avoid poorly ventilated areas like furnaces rooms, garages, and kitchens. Install the device twenty feet from a combustion source.
  • Don’t install smoke detectors in dusty, dirty or greasy areas.
  • Don’t install them close to ceiling fans and fresh air vents, as they can blow smoke away from the device.
  • Don’t install your smoke alarm in insect-infested areas, as they can clog the vents of the device and reduce its performance.
  • Install them at least 12 inches away from fluorescent light, as electrical noise can interfere with the device.
  • Don’t install in areas where the regular temperature is below 4 degree Celsius or above 38 degree Celsius.  

Smoke alarm placement

After figuring out the hallways and rooms to install your smoke detector, it is important that you know the right way to install it for optimal performance. As you know, smoke rises, so you should consider installing your detector within one foot from the ceiling.

Final note

If you are really serious about protecting your family and property from a fire, then you should consider installing smoke detectors in your home. To ensure that they work properly, you have to test them from time to time and change their batteries twice a year. Don’t attempt to fix your detector if it stopped working properly. Rather, seek the aid of a trained electrician so that he can help you ascertain what is wrong with the device.  

Before you go, did you know there is also other type of fire alarms? like this UV flame detectorOpens in a new tab., thermal detectorOpens in a new tab., and optical detectorOpens in a new tab.. Check them out.

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