Intruder Alarm System Using IR Sensor & 555 Timer

An intruder alarm system is a gadget that sounds an alert when it finds objects or people outside of a restricted area. Using an IR sensor and a 555 timer is a popular method for putting such a system into practice.

Any object with a temperature higher than absolute zero emits infrared radiation, which can be detected by an IR sensor. The sensor can determine how much infrared radiation is reflected by an item within its range of vision by employing an infrared transmitter and receiver. It indicates that something has moved or entered the space if the reflection changes.

An integrated circuit with great versatility, the 555 timer can produce a wide range of signals, including delays, oscillations, and pulses. The 555 timer can be programmed to generate a high or low voltage signal based on the condition of the IR sensor by connecting its output to the timer’s input. Subsequently, an alarm system, with a buzzer, light, or speaker, can be triggered by this signal.

With the help of an IR sensor and a 555 timer, we will build a basic intruder alarm system in this project. In addition, we will learn how to test and debug the system and investigate potential upgrades and additions.

Principle Behind Super Sensitive Intruder Alarm

The infrared receiver must receive the IR (infrared) rays that are constantly transmitted by the infrared transmitter. The transmitted infrared rays are reflected back to the infrared receiver by any obstruction that comes in front of the infrared sensor. When those IR beams reach the IR receiver, the Op-Amp’s output will rise. The 555 timer IC’s RESET (Pin 4) pin is connected to the Op-Amp’s output.

When the input voltage applied at the 555 timer IC’s RESET pin is low, the 555 timer IC’s output is low. The 555 timer integrated circuit generates a frequency that fluctuates on the resistors R1, R2, and capacitor C3 when the input voltage at the RESET pin is high.

The 1uF/16V electrolytic capacitor filters the 555 timer IC’s output before sending it to the buzzer.

Various infrared sensors are positioned at various points within the housing complex. All of these infrared sensors’ outputs are connected to a common 555 timer IC’s RESET pin. The buzzer will begin to beep and the reset pin of the 555 timer IC will become high when any of these sensors identify an intruder.


Intruder Alarm System Using IR Sensor & 555 Timer

Circuit Schematic



NE555 Timer IC
LM358 Op-Amp
10K Preset
IR Transmitter
IR Receiver
Red Led
Ceramic Capacitors (0.1uF, 0.01uF)
Electrolytic Capacitor – (1uF, 16V)
10KΩ, 1KΩ, 100Ω Resistor
330Ω Resistor (x2)
+5V Power Supply

Circuit Connection

555 Timer IC

Here, the 555 timer integrated circuit serves as a free-running oscillator. When a high pulse is supplied to the RESET pin, it will produce frequency. The resistor values R4 and R5 and the capacitor C3 are adjusted to change the frequency that the 555 Timer IC generates.

Here The 555 timer ICs’ pins 2 and 6 are shorted to enable triggering following each timing cycle. Capacitor C3 in this circuit charges via resistors R4, R5, and R6, and discharges through resistor R5.

LM358 Op-Amp

Two operational amplifiers make up each LM358 integrated circuit. Two inputs (one non-inverting and one inverting) and one output are present in every Op-Amp. When the non-inverting input exceeds the inverting input, the output will be high; conversely, when the inverting input exceeds the non-inverting input, the output will be low.

Infrared Transmitter

This infrared transmitter operates between 2 and 3 volts at its working voltage. We attach a resistor in series with an IR transmitter to lower the residual voltage.

Infrared Receiver

It is always connected to the circuit in reverse bias. When it is exposed to infrared (IR) radiation, it behaves almost like a closed circuit and becomes resistive when not exposed to any IR radiation.

Operation of Super Sensitive Intruder Alarm

The circuit must first have all of its parts connected and powered by +5V.

Move any obstruction in front of the infrared sensor after that. The circuit will then become high at that point after it has caught the sent infrared light. That’s when the buzzer will start beeping.

Additionally, the circuit will stay low if there isn’t anything blocking the IR sensor. Thus, there won’t be a beep.

That is how the circuit will function as a whole.


For security reasons, intruder alarm systems are installed in homes and workplaces.


In addition, this circuit emits sound when anything inanimate is in front of the infrared sensor.

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