Working Principle of Fire Alarm

Now-a-days a fire alarm system always comes with many other detection system in one package. It can detect smoke, fire, exotic gases etc. A fire alarm system is an active fire protection system that controls all fire alarm modules in a building. It includes alarm triggering devices,  alarm notification devices (sirens or devices emitting loud repetitive sounds), fire protection devices (sprinkler systems),fire extinguishers, power supplies and cables. But how do they work? Together,they work through an electric circuit, which turn on only in response to the environmental change due to fire, smoke or gases.

Comparison of 7 fire-alarms for your home

Nest (S3003LWES) Protect Smoke and Carbon Monoxide Alarm1 pounds3 AAWhite5.3 x 1.5 x 5.3 inSee Details
First Alert Smoke Detector1 lb2 AAWhite5.7 x 5.7 x 2.4 inSee Details
Kidde i4618AC Battery Backup Firex Hardwire Ionization Smoke Detector0.6 lb9-Volt batteryMulti2 x 6 x 6 inSee Details
Kidde Sealed Lithium Battery Power Carbon Monoxide Alarm with Digital Display C3010DN/ARequiredWhite4.5 x 1.5 x 2.75 inSee Details
Nighthawk AC Plug-in Operated Carbon Monoxide Alarm1.07 pounds9-Volt batteryWhite6.06 x 3.75 x 1.75 inSee Details
Kidde 21008873 Battery Operated Digital Display9.1 ounces3 AAMulti4.5 x 1.5 x 2.75 inSee Details
First Alert CO710 Carbon Monoxide Detector7.2 ounces1 lithiumWhite0.94 x 4.75 x 2.63 inSee Details


The fire alarm system can be activated automatically by smoke detectors, heat detectors or manually. These sensors are configured to detect certain levels of heat or smoke that may indicate a fire. A loud ring or siren, sometimes accompanied by flashing lights or flashing lights for the hearing impaired, triggers a sound to alert occupants of the building. Now, the systems are getting smarter. The system can now inform the occupant verbally,even send message to the local fire control service of the city. To fully understand how a fire alarm system works, let’s take a closer look at its components. In a fire alarm system, there is always a smoke detector to detect smoke or fire. How does a smoke detector work? There are two main types of fire alarm systems used in homes: ionization identifiers and photoelectric (optical)detectors.

Ionization identifiers

Inside those that are ionized, there is a two-plate ionization chamber and a source of ionizing radiation. The alarm battery sends a voltage to the plates, charging a positive and a negative. The source of radiation, a small sum (about 1 / 5000th of a gram) of an isotope called Americium-241, rots and discharges alpha particles (subatomic particles composed of two protons and two neutrons) at a constant speed. Because the particles pass through the chamber, they ionize or emit electrons, visible oxygen and nitrogen atoms all around the charge. The recently free electrons,which have a negative charge, are introduced into the positively charged plate,and the atoms, resolutely charged, are attracted into the negative plate. This maintains a constant current between the two plates. When the smoke enters the chamber, it disrupts this small ionization movement and reduces or cuts the current between the plates, triggering the alarm. Here is how the alarm works.

Photoelectric (optical) detectors

The optical smoke detector detects smoke using light sensors (infrared LEDs). The optical detector has slots around its housing that lead to the main sensing chamber. An invisible infrared light beam, burst into the chamber through a light emitting diode (LED). The same chamber contains a photocell, which is an electronic light detector that generates electricity when light falls on it. Normally, when there is no smoke, the light beam of the LED does not reach the detector. An electronic circuit, monitoring the photocell, detects that everything is fine and that nothing happens. The alarm remains silent. But if a fire breaks out, the smoke enters the chamber and diffuses a part of the light beam into the photocell. This triggers the circuit,triggering the ear-hurting acute and unpleasant alarm that wakes you up and saves your life. Even a motion detector can be interfaced with this device.

A few fire-alarms for your home

Nest (S3003LWES) ProtectSmoke and Carbon Monoxide Alarm

It’s time to wait longer than your smoke detector. Nest Protect has been redesigned from the inside out. It has a split-spectrum sensor, automatic tests and a lifetime of up to 10 years. It is also the first home alarm you can activate from your phone without additional hardware. And it tells you what’s wrong and can even alert your phone. Nest products are designed to work together. And they can even work at home with lights, locks and other products. Nest Protect can alert the Nest Thermostat when it detects carbon monoxide and the thermostat can turnoff the furnace to help reduce leaks safely. Nest focuses on making simple,human and delicious things. This is how we create a well thought house: a house that cares for its people and the world around them.

You will be delighted with the clarity of the voice coming from the unit informing you that a test would begin in 10 seconds. The voice was also kind enough to let you know that you had 10 seconds to cancel the alarm test because the alarm would be loud. The alarms themselves (smoke and carbon monoxide) look like a traditional detector. They are accompanied by a color-coded warning that makes it easier to understand what is happening. In addition, depending on the severity of the detection, the color will change (ie, if the toast burns, the color will be different from that used if your sofa is on fire). The unit can detect the amount of smoke in the room and gives you the option to turn off the silence from your phone / tablet. In addition, if the alarm goes off when you are not there, you will receive an alert.

Other interesting features are: 1. The low battery warning will never go off in the middle of the night (major selling point for many) Plus, alerts are sent to your phone, so you do not have to to count on annoying beeps to know if the batteries are exhausted. 2. The installation has been surprisingly easy for the wired version and can take about five minutes. However, the square shape of the unit did not completely cover the marks left by the uninstallation of the old round unit. 3. You will love the motion detection ability. If you go under the unit at night, a soft white glow will brighten your path. A small feature, but pretty cool.

The First Alert BRK 3120B

The First Alert BRK3120B Wire Smoke Detector includes a battery backup that continues to protect you in the event of a power failure. It is designed for residential use as well as for institutions such as hospitals, hotels, dormitories and multi-family dwellings. This alarm is inter-connectable and can be connected to up to 18 compatible devices so that all alarms are triggered when an alarm occurs. This alarm emits a powerful 85 decibel spread spectrum alarm for people with hearing loss. The First Alert dual sensor smoke detector includes photoelectric and ionization sensors for increased detection. The photoelectric sensor detects fires of objects such as lit cigarettes on furniture or garbage cans, while the ionization sensor detects fast fires such as kitchen fires or fuels. A button deactivates nuisance alarms and also tests detector functions, while the LED sindicate whether the alarm detects smoke. The memorized alarm indicator automatically identifies which unit triggered the alarm, even after the conditions that triggered the alarm disappear. In addition, an end-of-life signal improves your safety by telling you when to replace the unit.

It must be placed at a specific location in your home.Place at least 10 feet from the kitchen / stove and ceiling or top on a wall,no more than 10 inches from the top. Carbon monoxide alarms can be placed anywhere, not just on the ceiling or on a wall. They should be replaced every 5 to 7 years. Stay in the kitchen and garage, but make sure you have the right degree for the type of fire that might occur. Have at least one if your house has more than one story. Each room needs 2 escape routes; in most rooms, it’s the window, so have a ladder nearby.

Price for a multi-pack, my house uses six smoke detectors. Content: as stated in the advertisement, in addition to six plastic cups and six instruction guides. The 9-volt batteries provided are EverReady.Dust covers are only used after installation in building areas that generate plaster dust or drywall. Do not use the cups daily. The black, white and neutral connector pins are clearly marked on the reverse label for easy identification. The wire insulation is pre-cut to ½ “but I stripped mine to 3/4” for better wire contacts. Happy to remove all old units and rewire the information instead of using adapters, the electrical junction boxes being very narrow, the addition of adapters would have made the area more congested. The dome-shaped top lid looks flexible. Handle it carefully to avoid excessive pressure when installing and replacing the battery. No new screws are included for mounting the base on the electrical junction box. So use your existing screws and not a circuit breaker.

Batteries: Instructions are on page 4 of the attached printed brochure, subtitle REGULAR MAINTENANCE. WARNING states do NOT use 9-volt rechargeable batteries. When installation is complete, turn on the projector again, the green light on each unit is on to confirm power, and then remove the clear plastic tape to activate the battery. Noticed that I had to hold the test button a few seconds the unit to tweet twice, then release,otherwise they were not reset and continued to whistle. The long wait solved the problem – the instructions for the best reset method are unclear. An installation at home, without risk of theft or tampering, has therefore personally decided not to use the locking pins provided on the battery compartment cover or the ceiling mount – the use of the locking pin is optional.

Kidde i4618AC Battery BackupFirex Hardwire Ionization Smoke Detector

The AC / DC direct connect smoke detector with front access battery door simplifies the replacement of batteries that can be interconnected with up to 18 Firex devices and an 85 decibel alarm. AC or DC powered smoke detector operating on a 120-volt power source with a 9-volt battery backup. This alarm uses ionization detection technology. Ion detection alarms can detect invisible fire particles (associated with fires) earlier than photoelectric alarms. Photoelectric detection alarms can detect visible particles (associated with fires that are burning) faster than ionization alarms.

The adapters fit easily although it took a very firm hand pressure to repair them. It is actually an adapter to clip on both sides,on the old connection, then on the detector. No tools are needed except for a screwdriver to loosen the old mounting bracket and replace it with the new one.The mounting brackets easily fit existing screws from the old detector mounting plate. The mounting plates being a bit larger, the perfectly treated paint lines have bypassed the old detectors (no retouching necessary).

Again, it took very firm hand pressure to insert the adapter on the new smoke detector. In addition, the detector emitted a loud beep that surprised me at first. Connected correctly, the fire goes green. I fit is not connected properly, the flashing red light will force you to press harder to turn on the connector and turn it green.

The detector, connected by wires, simply and comfortably rotates in the mounting bracket. It will take you less than 10 minutes per detector, and of course, it was easier after the first that you were scared at first to support very hard to put everything in place. participates in the Amazon Services LLC Associate Program, which is an affiliate advertising program designed to provide a means for websites to earn advertising fees by advertising and linking to