A fire alarm system uses visual and audio signals to warn of fires. It includes devices installed throughout buildings to detect smoke and fire and alert occupants. There are three main types of fire alarm systems: ionization, photoelectric, and combination alarms. According to statistics, over 350,000 home structure fires occurred from 2012-2016 in the U.S., resulting in over 2,500 deaths and $6.5 billion in property damage. A simple fire alarm circuit project uses a thermistor to detect temperature increases from fire, which triggers an operational amplifier to activate a buzer and warn occupants. Properly installed and maintained fire alarm systems improve safety and reduce loss of life and property damage from fires.

1. Complex Engineering Activity 3
Fire Alarm System

2. What is a Fire Alarm System?
 A fire alarm is a unit made of several devices, which uses visual and audio
signalization to warn people about a possible fire, smoke, or carbon monoxide
occurrence in the area of coverage. Fire alarms are usually set in fire alarm
systems to provide zonal coverage for residences and commercial buildings. The
warning signal is either a loud siren/bell or a flashing light, or it can include both.
Some fire alarm systems use additional warnings, such as sending a voice
message or making a phone call.
 The first step to protecting lives and property from the consequences of fires is
setting up a high-quality fire alarm system. After installing it, it’s important that you
keep the system well-maintained to make sure it’s always working at its best.

3. Types of Fire Alarm System
There are three main types of fire alarm
monitoring systems:
1. Ionization
2. Photoelectric
3. Combination Alarms

4. According to the National Fire Protection
Association
 355,400 home structure fires happened between 2012-2016
 2,560 civilians died due to home fires
 11,670 civilians injured due to fires
 6.5 billion dollars in property damaged in fires
 On average, seven people die in home fires per day

5. Project Circuit

6. Components
 1 x 10 K Thermistor
 1 x LM358 Operational Amplifier (Op – Amp)
 1 x 4.7 KΩ Resistor (1/4 Watt)
 1 x 10 KΩ Potentiometer
 1 x Small Buzzer (5V Buzzer)
 Connecting Wires
 Mini Breadboard
 9V Power Supply

7. Circuit Design
 The design of the Fire Alarm Circuit with Siren Sound is very simple. First, connect the 10 KΩ
Potentiometer to the inverting terminal of the LM358 Op – Amp. One end of the POT is connected
to +9V, other end is connected to GND and the wiper terminal is connected to Pin 2 of Op – Amp.
 We will now make a potential divider using 10 K Thermistor and 4.7k KΩ Resistor. The output of this
potential divider i.e. the junction point is connected to the non – inverting input of the LM358
Operational Amplifier.
 We have chosen a small, 5V buzzer in this project to make the alarm or siren sound. So, connect the
output of the LM358 Op – amp to the 5V Buzzer directly.
 Pins 8 and 4 of the LM358 IC i.e. V+ and GND are connected to +9V and GND respectively.

8. Working
 We will now see the working of the simple Fire Alarm Circuit. First thing to know is that
the main component in detecting the fire is the 10 K Thermistor. As we mentioned in
the component description, the 10 K Thermistor used here is a NTC type Thermistor. If
the temperature increases, the resistance of the Thermistor decreases.
 In case of fire, the temperature increases. This increase in temperature will reduce the
resistance of the 10 K Thermistor. As the resistance decreases, the output of the voltage
divider will increase. Since the output of the voltage divider is given to the non –
inverting input of the LM358 Op – Amp, its value will become more than that of the
inverting input. As a result, the output of the Op – Amp becomes high and it activates
the buzzer.

9. Benefit's of Fire Alarm System
 Safety Benefits
The main advantage and function of a fire alarm system is to ensure ultimate
safety. They help warn and keep people safe and reduce the amount of destruction to
a building.
 Life Safety
This is probably the major reason as to why a business will install a fire detection
system. A high quality and advanced fire detection and alarm system will be able to
warn the employees of a building that they need to get out of the building when a fire
is starting and where the fire is in the building.
 Property Safety
Fire detection systems increase response times, as they are able to alert the
correct people in order to extinguish the fire. This thus reduces the amount of damage
to the property. Fire detection systems can be connected to sprinklers that will
automatically respond when a fire is detected.