Safety Tools

Photoelectric Smoke Detectors

Are you indecisive on which smoke detector to go for? If yes, then this guide would be an inspiring read for you. We have written this guide on the photoelectric smoke detectors. In this guide, you’ll find all the information you need to know about the photoelectric smoke detector.

As you read through, be sure to take note of the main points. So it is expected that after reading through this guide, you should no longer have that indecision problem.

What Is a Smoke Detector

Smoke alarms are compulsory in most homes and units these days to ensure the safety of the occupants in the event of a fire.

A smoke detector is a device that senses the presence of smoke in a building and warns the occupants, enabling them to escape a fire before succumbing to smoke inhalation or burns. Equipping a home with at least one smoke detector cuts in half the chances that the residents will die in a fire

Two basic types of smoke detectors are currently manufactured for residential use. The photoelectric smoke detector uses an optical beam to search for a smoke. When smoke particles cloud the beam, a photoelectric cell senses the decrease in light intensity and triggers an alarm. This type of detector reacts most quickly to smoldering fires that release relatively large amounts of smoke.

Photoelectric Smoke Detectors

A photoelectric smoke detector is a light detector that uses a light beam and electrical photocells (photodiodes) to track smoke particles.

Photoelectric, or optical smoke detector, contains a source of infrared, visible, or ultraviolet light — typically an incandescent light bulb or light-emitting diode (LED) — a lens, and a photoelectric receiver — typically a photodiode. In spot-type detectors, all of these components are arranged inside a chamber where air, which may contain smoke from a nearby fire, flows.

In large open areas such as atria and auditoriums, optical beam or projected-beam smoke detectors are used instead of a chamber within the unit: a wall-mounted unit emits a beam of infrared or ultraviolet light which is either received and processed by a separate device or reflected the receiver by a reflector.

In some types, particularly optical beam types, the light emitted by the light source passes through the air being tested and reaches the photosensor. The received light intensity will be reduced due to scattering from particulates of smoke, air-borne dust, or other substances; the circuitry detects the light intensity and generates the alarm if it is below a specified threshold, potentially due to smoke.

Light beams (made of an incandescent bulb or infrared LED light that helps to collect the light source into a beam) in the smoke detector will reflect onto the photocells.

The photocells are arranged at a right-angle to the beam of light so that light entering the chamber does not typically attract the photocells.

This device aims a focused light source into a sensor chamber; when smoke enters the chamber, it reflects light, which then triggers the alarm. Photoelectric smoke detectors are best at detecting large smoke particles from slow, smoldering fires.

When smoke particles enter the optical chamber, these particles interfere with the light beam (i.e., the lights reflect off of the smoke particles) and then make contact with the electrical photocells. This contact increases the electrical charge in the detector to a threshold level, which initiates an alarm signal.

Photoelectric smoke detectors are typically installed in large commercial and social settings, including gymnasiums and auditoriums.

These detectors, according to several university studies, are significantly more effective in picking up smoldering fires. With today’s pervasive use of fire retardant materials, most fires actually smolder for a significant amount of time before growing into a flaming-fire.

The photoelectric smoke detectors are quicker activating with these smoldering fires and substantially the same in fast-burning fires. By utilizing a single sensor photo-electric smoke detector residents may be notified between 2 and 40 minutes earlier, based on university studies.

Photoelectric smoke alarms have a distinct advantage over the Ionisation version in that occupants are alerted quicker to smoldering smoke allowing time to escape from the premises. Most house fires start with a smoldering fire initially. Ionization alarms react when the house is well alight, significantly reducing the number of times occupants have to evacuate a burning home.


  • Ideal for detecting dense smoke
  • Less prone to false alarms from cooking fumes or shower steam
  • Do not contain radioactive materials, making them safer for use
  • Suitable for general use
  • Good for smoldering fires and dense smoke
  • Not as prone to cooking nuisance alarms


  • Sensitive to dust particles and insects, meaning that regular maintenance is needed
  • More expensive
  • Expensive to maintain
  • Require more current to operate (they are typically wired to a 110-volt power source)

The light beam in a typical photoelectric smoke detector can be obscured in two ways:

  • The light-obscuring method

Dense smoke tends to only obscure part of the light beam, whereas less-dense smoke particles can move around more freely, obscuring more of the light beam and therefore, impacting the alarm system. In some instances, a mirror is used to position the light beam to measure the area of coverage of the smoke particles.

  • The light-scattering principle

A light scattering principle is based on the idea that smoke particles entering the sensing chamber strike the light beam and scatter the light onto photoelectric particles.

When Is a Photoelectric Smoke Detector Best?

Photoelectric smoke alarms respond fastest to smoldering fires that begin slowly and burn without a flame for a long period of time. It’s no secret that many deaths from residential fires occur as a result of smoke inhalation rather than flames.

Being able to detect smoke early can be a lifesaver, helping families to escape before the flames have even started and before potentially life-threatening smoke inhalation. These types of fires often occur when small flames from things like candles or cigarettes are left unattended. The Cause fewer false alarms from cooking in the kitchen or steam in bathrooms, and they do not contain radioactive material.

How Do Photoelectric Smoke Detectors Compare To Other Smoke Detectors?

Other popular technologies for smoke detectors are ionization alarms and dual-sensor smoke detectors. The dual-sensor smoke detector has both ionization and photoelectric technology inside. Ionization smoke alarms are best for detecting rapid flame fires, while photoelectric smoke alarms protect against slower, smoldering fires.

Should I Have A Photoelectric Smoke Detector?

It’s safe to say every home should have a photoelectric smoke detector. While the ionization smoke detector has been proven more effective in detecting flaming fires, photoelectric alarms outperform them when it is a smoldering fire. For best protection, it is recommended to have both types of fire alarms throughout your home.

The upside is that there will be less risk of false alarms since they have a higher threshold of smoke tolerance. The downside is that in certain situations like flaming fires that do not produce large smoke particles, by the time it sounds the alarm, the fire may have grown too large to be easily tackled.

If you’re looking for an optical smoke detector, get one with as many of these features as possible:

  • Bright strobe escape lights – During an actual fire, visibility is extremely poor so these lights are useful.
  • Remote controllable mute button to silence the alarm in case of false alarms.
  • Lithium battery operated. Lithium batteries can last 10-15 years without changing.
  • Secure battery compartments with auto-lock to prevent children tampering with them.
  • Alarm notification in case the batteries need changing.

What’s inside the detector?

Once Freymann and Tolman had discovered their fiber, it was relatively simple to build a part-electrical, part-mechanical smoke detector around it:

  • A length of the magic fiber (yellow) is stretched around a wheel (red) inside a metal container (gray) with holes at the bottom through which smoke can enter.
  • The fiber is attached to a pivoting lever (light blue), held in place by a spring (purple).
  • The blue lever holds another pivoting lever (green) in place.
  • The green lever supports an electrical contact (dark blue) and holds it well above a second identical contact.
  • The two contacts connect to a battery-powered bell or another electrical alarm circuit.

You can create the safest environment possible for your family by installing a mix of photoelectric and ionization smoke detectors. It’s too risky to go with one and not the other because there is no way to predict what type of fire threat your home may experience.

Some smoke detectors utilize both ionization and photoelectric technologies. These types of smoke detectors are known as “dual” smoke detectors and are widely available at home improvement stores and online at a variety of price points and from several brands.

As a homeowner, you want to do all you can to take advantage of the potentially lifesaving technology available for smoke and fire detection. No matter the type of smoke detector you select, it’s crucial that you test your detector, routinely.


In summary, it must be stressed that, despite the functional differences and levels of sensitivity between photoelectric and ionizing smoke detectors, both devices are acceptable as life-saving smoke sensors.

Safety Tools

Interconnected Or Stand Alone Smoke detectors?

Are you having problems deciding whether to install an interconnected smoke detector or a stand-alone smoke detector? Look no further. This guide aims to show you which you should go for. So seat down, and read through this review keenly.


A smoke detector is a device that senses smoke, typically as an indicator of fire. Commercial smoke detectors issue a signal to a fire alarm control panel as part of a fire alarm system, while household smoke detectors, also known as smoke alarms, generally issue an audible or visual alarm from the detector itself or several detectors if there are multiple smoke detectors interlinked.

Smoke detectors are housed in plastic enclosures, typically shaped like a disk about 150 millimeters (6 in) in diameter and 25 millimeters (1 in) thick, but shape and size vary. Smoke can be detected either optically (photoelectric) or by physical process (ionization). Detectors may use one of the two or both sensing methods.

Sensitive alarms can be used to detect, and deter, people smoking in areas where smoking is banned. Smoke detectors in large commercial and industrial buildings are usually connected to a central fire alarm system.

Domestic smoke detectors range from individual battery-powered units to several interlinked units with battery backup. With interlinked units, if any of them detects smoke, all of the alarms will trigger even if household power has gone out.

The risk of dying in a home fire is cut in half in homes with working smoke alarms. The US National Fire Protection Association reports 0.53 deaths per 100 fires in homes with working smoke alarms compared to 1.18 deaths without (2009–2013). Some homes do not have any smoke alarms and some homes do not have any working batteries in their smoke alarms.

Installation and placement of smoke detectors

In the United States, most state and local laws regarding the required number and placement of smoke detectors are based upon standards established in NFPA 72, National Fire Alarm and Signaling Code. Laws governing the installation of smoke detectors vary depending on the locality.

However, some rules and guidelines for existing homes are relatively consistent throughout the developed world. For example, Canada and Australia require a building to have a working smoke detector on every level.

The United States NFPA code cited in the previous paragraph requires smoke detectors on every habitable level and within the vicinity of all bedrooms. Habitable levels include attics that are tall enough to allow access. Many other countries have comparable requirements.

In new construction, minimum requirements are typically more stringent. All smoke detectors must be hooked directly to the electrical wiring, be interconnected, and have a battery backup. In addition, smoke detectors are required either inside or outside every bedroom, depending on local codes.

Smoke detectors on the outside will detect fires more quickly, assuming the fire does not begin in the bedroom, but the sound of the alarm will be reduced and may not wake some people. Some areas also require smoke detectors in stairways, main hallways, and garages.

A dozen or more detectors may be connected via wiring or wirelessly such that if one detects smoke, the alarms will sound on all the detectors in the network, improving the likelihood that occupants will be alerted even if smoke is detected far from their location. Wired interconnection is more practical in new construction than for existing buildings.

In the UK the installation of smoke alarms in new builds must comply with British Standard BS5839 pt6. BS 5839: Pt.6: 2004 recommends that a new-build property consisting of no more than 3 floors (less than 200 square meters per floor) should be fitted with a Grade D, LD2 system.

Building Regulations in England, Wales, and Scotland recommend that BS 5839: Pt.6 should be followed, but as a minimum a Grade D, LD3 system should be installed. Building Regulations in Northern Ireland require a Grade D, LD2 system to be installed, with smoke alarms fitted in the escape routes and the main living room and a heat alarm in the kitchen; this standard also requires all detectors to have a mains supply and a battery back up.

Keep Smoke Detectors Working Properly

Find important information and tips for keeping your smoke detectors working properly below:

  • Test your smoke detectors at least once a month by using the detectors’ test button.
  • Replace the batteries in your smoke detectors regularly, or as soon as it chirps, warning that the battery is low (Reminder: “Change your clocks, change your batteries!”).
  • Regularly vacuuming or dusting your smoke detectors and following manufacturer instructions can help keep them working properly.
  • Replace your smoke detectors every 10 years.
  • Never borrow a battery from a smoke detector.
  • Make sure that everyone in your home can hear and recognize the alarm sound your detector(s) makes and how to react immediately.

You should note that smoke detectors can be further divided into two:


These detectors can easily have defective or worn-out batteries and need to be checked monthly. You never want to put old batteries into your fire alarms or smoke detectors.

You will want to frequently check that the batteries are working properly.


These detectors are powered by your home’s electrical system but tend to also have backup batteries so they still work if there is a power outage. Even though this device mainly uses your home’s electricity, you still need to check the batteries.

Hardwired smoke detectors still need to be tested monthly. This helps ensure that both the parts and batteries are working properly

What is an Interconnected Smoke Detector?

A hardwired smoke detector can communicate wirelessly with other compatible alarms to create a fire alarm system (additional alarms sold separately). When one alarm is triggered, all connected alarms will sound

Integrated battery backup allows continuous detection during power outages.

Benefits of Interconnected Smoke Detectors

When smoke and carbon monoxide (CO) alarms are interconnected, each alarm can now tell you when there’s smoke or carbon monoxide in any room that has a smoke/CO alarm. A traditional alarm can alert you to the presence of smoke, fire, or carbon monoxide, but it can only detect the area around it.

  • Interconnected alarms are safer

Interconnected smoke alarms are safer than standalone smoke alarms because they let you know about an emergency sooner. Even if you’re in the house, you may not be close to the area where the fire started. If you’re in the basement, you may not hear an alarm in the bedroom. According to the National Fire Protection Association (NFPA), the majority of fatalities from US home fires were located in a different room than where the fire started.

  • Required for new home constructions

Because of their many benefits, including safety and early warning, many states now require interconnected smoke alarms for new home construction.

  • Wireless Interconnect

In the past, interconnection had to be hard-wired between smoke/carbon monoxide alarms. Now smoke/CO alarms can be interconnected wirelessly, without requiring expensive retrofits. With wireless interconnect, you can easily retrofit existing homes and get them up to code.

  • Full Home Coverage

When it comes to staying safe from home fires, time is of the essence, with only a couple of minutes to escape from a house fire. If a fire starts on the top floor of your home and you are in the basement, there’s a chance you may not be able to hear the alarm going off.

If you have an interlinked smoke alarm system in your home, the basement smoke alarm will sound when the top floor alarm goes off.

You will be able to hear the alarm regardless of where you are, compared to where the initial alarm is. In fact, according to the National Fire Protection Association (NFPA), the majority of fatalities stemming from home fires in the United States were located in a different room than where the fire started.

An interconnected smoke alarm system will help give you and your family peace of mind knowing your entire house is fully protected.

A survey was carried out, on whether smoke detectors improve safety:

Interconnected smoke alarms increase safety;

In a Consumer Product Safety Commission (CPSC) survey of households with any fires, including fires in which the fire department was not called, interconnected smoke alarms were more likely to operate and alert occupants to a fire.1 People may know about a fire without hearing a smoke alarm.

  • When smoke alarms (interconnected or not) were on all floors, they sounded in 37% of fires and alerted occupants in 15%.
  • When smoke alarms were not on all floors, they sounded in only 4% of the fires and alerted occupants in only 2%.
  • In homes that had interconnected smoke alarms, the alarms sounded in half (53%) of the fires and alerted people in one-quarter (26%) of the fires.


Above all, you should own at least one smoke detector in your home. However, to be more on the safer side, install an interconnected smoke detector. This will help to inform all the persons in the building when there is smoke. Protect what matters most by installing reliable protection in your home today.