Home Security Alarm Using PIR Sensor & Arduino 

Working of PIR Sensor:
PIR sensors are more complicated than many of the other sensors explained in these tutorials (like photocells, FSRs and tilt switches) because there are multiple variables that affect the sensor’s input and output.

The PIR sensor itself has two slots in it, each slot is made of a special material that is sensitive to IR. The lens used here is not really doing much and so we see that the two slots can ‘see’ out past some distance (basically the sensitivity of the sensor). When the sensor is idle, both slots detect the same amount of IR, the ambient amount radiated from the room or walls or outdoors. When a warm body like a human or animal passes by, it first intercepts one-half of the PIR sensor, which causes a positive differential change between the two halves. When the warm body leaves the sensing area, the reverse happens, whereby the sensor generates a negative differential change. These change pulses are what is detected.

Working of the Project:

Components Required:
Arduino UNO Board
PIR Sensor HC-SR501
LDR
1K Resistor-2
LED
Buzzer
Potentiometer
lCD display
9V Battery
Arduino Cable
Jumper wires

The circuit is in fact a dark activated switch that measures the ambient light level and will enable the system only when the ambient light level is below a threshold value. Here an LDR (Light Dependent Resistor) is used to measure the light level. The alarm system is triggered when a “Logic High (H)” level signal is detected at its sensor input port.

The best sensor you can use to detect an intrusion is the Passive Infrared (PIR) Sensor. The PIR Sensor detects the motion of a human body by the change in surrounding ambient temperature when a human body passes across, and effectively controls the switching when it detects a moving target.