Safety Tools

Ionization Smoke Detectors

Have you wondered how ionization detectors work? This focuses on ionization smoke detectors. With the aid of this guide, you should have an idea of how ionization smoke detectors work. The importance of knowing how they work is that you would be able to determine if they are a good fit for you and your household. Therefore, you should endeavor to read through so you can gather all the information you need about ionization smoke detectors.

What is a smoke detector?

Smoke detectors are common household items that keep you and your family safe by alerting you to smoke in your home. All smoke detectors consist of two basic parts: a sensor to sense the smoke and a very loud electronic horn to wake people up.

Smoke detectors can run off of a 9-volt battery or 120-volt house current. While it can be easy to forget to check and test smoke alarms regularly, it is important to ensure that they are not only properly maintained but also correctly installed.

How do Smoke Detectors Work?

Since smoke rises, smoke detectors are always placed on the roof for ideal detection. There are two common types of smoke detectors to choose from photoelectric and ionization. Photoelectric sensors use a beam of light within the detector to sense any smoke in the air.

The beam will shoot in a straight line when the air is clear. In the presence of smoke, the light will scatter, this is when the alarm will go off. Ionization detectors, on the other hand, use a chamber with a small electrical current. When smoke enters the chamber and the level of ions in the air changes, the electrical current drops and the alarm will sound.

Each function is beneficial in different instances and because of this, one is not necessarily better than the other. It is, however, recommended to have one of each of these functions on each floor of your home and in high-risk areas, such as the kitchen or near fireplaces and heating appliances.

A typical household smoke detector is disc-shaped and powered by a disposable battery. There are two types of smoke detectors – photoelectric and ionizing.

Generally, home smoke detectors work in one of two ways:

Ionization detectors respond best to fast, raging fires and flames. They use a small amount of radioactive material passing between two electrically charged plates to create an ionization chamber. This ionizes the air and creates a current that flows between the plates. Smoke particles disrupt the flow of ions, reducing the current and triggering the alarm.

Photoelectric detectors respond best to smoky fires that start with a long period of smoldering. They rely on a photoelectric sensor and a light source to detect smoke. When smoke seeps into a compartment in the detector, it covers the light beam and reflects light onto the light sensor, causing the alarm to sound.


Ionization smoke detectors use a small amount of radioactive material, americium-241, which ionize smoke particles in the air. This type of smoke detector is more common because it is inexpensive and better at detecting the smaller amounts of smoke produced by flaming fires.

Inside an ionization detector is a small amount (perhaps 1/5000th of a gram) of americium-241. The radioactive element americium has a half-life of 432 years and is a good source of alpha particles.

The functionality principle of the radioactive isotope americium-241 involves the emission of alpha particles, which ionize air particles in the sensing chamber so that they conduct electricity.

During the emission of the alpha particles into the air, a chemical reaction occurs where air molecules in the collecting chamber are ionized and, as a result, carry an electrical charge. Smoke particles surrounding the ionizing smoke detector enter the collecting chamber and attach to the ions, making it more difficult for the ions to deliver an electrical charge.

A decrease in the electrical flow is detected by a circuit that then triggers an alarm system. This type of smoke detector is ideal for detecting invisible particles produced by fires, and so will work much faster and be more sensitive compared to a photoelectric detector.

Alpha particles are used for the ionizing smoke detector as they have high ionizing potential. Although there are concerns that this type of smoke detector emits radiation, the alpha particles used have low penetrative potential and so will not pass through plastic material.

The standard amount of americium-241 used in the ionizing smoke detector is not enough to raise regulatory concerns – a standard amount of radioactive americium-241 is made up of 37KBq or 1ìCi, which is enough to detect smoke particles without contaminating the outer surface of the detector.

Another way to talk about the amount of americium in the detector is to say that a typical detector contains 0.9 microcuries of americium-241. A curie is a unit of measure for nuclear material. If you are holding a curie of something in your hand, you are holding an amount of material that undergoes 37,000,000,000 nuclear transformations per second.

Generally, that means that 37 billion atoms in the sample are decaying and emitting a particle of nuclear radiation (such as an alpha particle) per second. One gram of the element radium generates approximately 1 curie of activity (Marie Curie, the woman after whom the curie is named, did much of her research using radium).

Before being sold on the market, ionizing smoke detectors go through a radiation safety analysis to meet safety requirements. Compared to photoelectric smoke detectors, the ionizing smoke sensor is less expensive and more commonly used.

It is important to note that The ionization smoke detector has two ionization chambers, one open to the air, and a reference chamber that does not allow the entry of particles. The radioactive source emits alpha particles into both chambers, which ionizes some air molecules.

There is a potential difference (voltage) between pairs of electrodes in the chambers; the electrical charge on the ions allows an electric current to flow. The currents in both chambers should be the same as they are equally affected by air pressure, temperature, and the aging of the source. If any smoke particles enter the open chamber, some of the ions will attach to the particles and not be available to carry the current in that chamber.

An electronic circuit detects that a current difference has developed between the open and sealed chambers, and sounds the alarm. The circuitry also monitors the battery used to supply or back up power and sounds an intermittent warning when it nears exhaustion.

A user-operated test button simulates an imbalance between the ionization chambers and sounds the alarm if and only if the power supply, electronics, and alarm device are functional. The current drawn by an ionization smoke detector is low enough for a small battery used as a sole or backup power supply to be able to provide power for months or years without the need for external wiring.

Ionization smoke detectors are usually cheaper to manufacture than optical detectors. They may be more prone to false alarms triggered by non-hazardous events than photoelectric detectors and are much slower to respond to typical house fires.


  • Cheaper than photoelectric smoke sensors
  • Ionizing smoke alarms outperform photoelectric smoke alarms when detecting fast flaming fires with little visible smoke


  • Very sensitive, which can lead to false alarms as a product of cooking
  • Not as responsive to smoldering fires – they are minutes slower than photoelectric sensors in detecting smoke particles from smoldering fires
  • Some European countries, including France, and some US states and municipalities have banned the use of domestic ionic smoke alarms because of concerns that they are not reliable enough as compared to other technologies. Where an ionizing smoke detector has been the only detector, fires in the early stages have not always been effectively detected.
  • The use of radioactive material is a concern
  • The biggest disadvantage is that it contains a very small amount of radioactive material. These devices are probably not a problem unless they burn, in which case the Americium would be released in particulate form – an inhalation hazard.
  • Another big disadvantage is that it is a bit too sensitive. It can be vulnerable to nuisance alarms if placed too close to cooking. It goes off many times especially if it is kept near a kitchen. This can be very annoying especially if it happens repeatedly.

What Type of Fires Does an Ionization Alarm Detect?

Generally, ionization alarms are more responsive to flaming fires. The term “flaming” fires refers to fires resulting from flammable liquids, wood, or paper starting on fire. This type of fire produces a lot of flames with a limited amount of smoke.

Most house fires are categorized as fast-flaming fires, which is why ionization alarms are popular in homes. To be safe, we recommend having both types of home fire detectors installed, or installing combination alarms that detect multiple types of fires.

What You Can Do

  • Use a smoke detector in your home. It can save your life.
  • Never tamper with an ionization smoke detector. Never attempt to tamper with or remove the americium.
  • Replace the batteries. Replace the batteries in every smoke detector in your home twice a year. Most detectors are certified for a useful life of ten years. Check the expiration date on your smoke detector when you replace the batteries.
  • Throw away outdated ionization smoke detectors. Your community may have a separate recycling program for them.


Having gone through this review, you know what you stand to gain when you get an ionization smoke detector, and also what loss you’ll have. Nevertheless, it is always important to own a smoke detector in your home.

Safety Tools

How Many Smoke Detectors Do You Need?

Have you asked the question ‘how many smoke detectors do I need in my home?’ and got no reasonable answer? Well, today is your lucky day, as this guide is aimed at answering that question. Do make sure to read through this guide, and you’ll find out how many smoke detectors you need in your home.

What is a smoke detector?

A smoke detector is a device that combines smoke detection and a loud alarm together in one unit. The alarm sounds if it detects smoke in large amounts, like in a fire.

A smoke detector, when properly installed, tested, and maintained gives you an early warning of a fire, which increases your chances of getting out.

Which Type of Smoke Detector to Install in Your Home

Most homeowners don’t know that smoke detectors come in two types: ionization smoke detectors and photoelectric smoke detectors. At this point, you might wonder why anyone even bothers with knowing the difference.

While it may not be made for the most riveting article to read, knowing how ionization and photoelectric detectors work differently can potentially save your life one day.

The two most common are ionization and photoelectric smoke detectors, as was mentioned above. Understanding the difference between these two technologies will help you determine which type of smoke detector to install in your home.

  • Ionization-type alarms have a small quantity of radioactive material between two electrically charged plates, called electrodes. When this material ionizes the air, it causes a current to flow between the two electrodes. During a fire, smoke entering the chamber disrupts the flow of ions between the electrodes, setting off the alarm. Ionization smoke detectors are typically more responsive to flaming fires.
  • Photoelectric-type alarms use a beam of LED light to detect smoke during a fire. As smoke particles from a fire hit the LED beams, the sensor detects a break in the beam and is activated. Photoelectric alarms are typically better at detecting smoldering fires.

Because you won’t ever be able to predict whether a fire in your home will be a flaming fire or a smoldering fire, the NFPA recommends using both types of alarms for the best protection. Many manufacturers make alarms with dual sensors. The other option is to use a combination of ionization and photoelectric smoke alarms.

Should smoke detectors be on the wall or ceiling?

Since smoke rises, it’s best to install your smoke detector as high as possible – either on the ceiling or high on the wall. Just remember to leave at least three meters between the smoke alarm and any cooking appliances.


Smoke alarms actually don’t need a ton of maintenance. They can be checked once a month with batteries replaced at least once or even twice a year, according to the U.S. Fire Administration (USFA).

An easy way to remember to do this is to change your smoke detector’s batteries when you change your clocks for daylight savings time. However, be sure to review your smoke detector’s user manual, as you may need to check your devices more frequently.

You’ll also want to do a visual inspection to make sure your alarm indicator is on. This makes sure that both your hard-wired and battery-operated fire alarm is properly connected and the batteries are working.

You should also occasionally vacuum and dust around the alarm. This way your device is clear of insects and dirt which can tamper with the effectiveness of the alarm.

When you check your batteries, make sure there is no corrosion, if there is you need to change the batteries. You also want to calibrate and test your fire alarm sensors based on what the manufacturer suggests.

When you perform these regular checks on the alarm system and replace the batteries, then your smoke detector and fire alarm will be in the best condition possible.

Where should smoke alarms be located?

There are two important things to remember when deciding where to put smoke alarms:

  • Most fires start in the kitchen.
  • Smoke alarms are to warn people asleep in bedrooms.

Install at least one smoke alarm on every level of your home, including the basement (but not in unfinished attics).

  • Put smoke alarms in the hallways that lead to each bedroom.
  • On floors without bedrooms, install the smoke alarm in or near each living area such as dens, living, and family rooms.
  • Put a smoke alarm on the ceiling at the bottom of any staircase leading to the upper floors.
  • Mount the smoke alarm high on walls or ceilings (remember—smoke and hot gases rise). Wall-mounted alarms should be placed at least 10 to 30 cm down from the ceiling. The ceiling-mounted alarm should be placed at least 10 cm away from the nearest wall. If ceilings are pitched, install the alarm near the ceiling’s highest point.

Where shouldn’t smoke alarms be located?

Smoke alarms shouldn’t be put in kitchens, garages, or bathrooms. This is because dust, steam, and exhaust can set off nuisance alarms (see “What are Nuisances Alarms” below). Nuisance alarms are often called “false” alarms. However, it isn’t a false alarm because the smoke alarm is doing what it is supposed to.

Don’t install a smoke alarm near a window or register, where drafts can affect alarm operation and sensitivity.

How Many Smoke Alarms Do I Need in My House?

Unfortunately, there’s no one-size-fits-all answer here. The number of smoke alarms your house needs will depend on your personal circumstances. At the very least, you should have a smoke detector on every floor of your house. Of course the more smoke alarms you fit, the more protection you and your home will have.

However, When it comes to protecting your family, the first step is to be prepared. Smoke alarms are your first line of defense against a house fire by providing your family with an early alert, giving them time to safely escape.

At First Alert, we provide reliable protection you can trust to help protect what matters most. Do you know how many smoke alarms does your home need to be fully protected and what type is best for your needs? Here’s what you should know:

According to the National Fire Protection Association (NFPA), smoke alarms should be installed on every level of your home, including the basement. Fire detectors should also be installed inside every bedroom and outside of each sleeping area.

For example, two-story home with three bedrooms should have at least seven smoke alarms. Homes that have a set number of hardwired alarms can still place additional battery-operated smoke alarms throughout the house.

There is no such thing as having too many smoke alarms in your home! Just make sure fire detectors are properly placed in each area.


Check out these tips for installing your smoke detectors correctly below:

  • Install smoke detectors listed by a qualified testing laboratory on every level of your home, including the basement. Make sure there is a detector in or near every sleeping area.
  • Mount smoke detectors high on ceilings or walls. Remember that smoke rises therefore ceiling-mounted detectors should be installed at least four inches away from the nearest wall; wall-mounted detectors should be installed four to 12 inches away from the ceiling. If you have questions, contact your local fire department.
  • Don’t install smoke detectors near windows, outside doors, or ducts where drafts might interfere wither their operation.
  • Don’t paint your smoke detectors; paint or other decorations could affect their operation.

Don’t install the smoke detector

  • On windows or sliding doors as the winds and air may not pick up the heat of smoke or fire
  • In humid or moist areas including the bathroom
  • In areas that easily collect dust and dirt including unfinished attics
  • In cooler rooms such as sunrooms or porches
  • Near ceiling fans or air vents
  • In garages, as they are often not temperature-regulated and the cooler temperatures may not detect smoke or fire

Smoke Detector Safety Reminders

  • Test the smoke detector monthly. According to the National Fire Prevention Association, test your smoke detector monthly to make sure it’s working properly. Most smoke detectors have a one-press test button that shines a light or sounds a test alarm to let you know the detector is working properly.
  • Replace smoke detectors every 10 years. Most detectors only last up to 10 years before needing to be replaced. As a best practice, write down the installation date for each smoke detector so you’ll always know when to replace it.
  • Replace batteries annually. To make sure your smoke detector is working properly, change the batteries at least twice a year. As a best practice, change your smoke detectors when you change your clocks for Daylight Savings Time.
  • Keep the smoke detector clean. Make sure your detector is free of dust, dirt, paint and other particles that may prevent the detector from spotting and alerting you of smoke. Vacuum it at least once a year or more as needed.


After going through the above guide, we believe you have gotten clarity on the number of smoke detectors you need. Hence, when buying smoke detectors, you know how many you need, and the areas you need to place them.