PIR Motion sensors allow you to sense motion, almost always used to detect whether a human has moved in or out of the sensors range. They are small, inexpensive, low-power, easy to use and don’t wear out. For that reason, they are commonly found in appliances and gadgets used in homes or businesses. They are often referred to as PIR, “Passive Infrared“, “Pyroelectric“, or “PIR motion” sensors.

PIR Motion sensors are basically made of a pyroelectric sensor (which you can see above as the round metal can with a rectangular crystal in the center), which can detect levels of infrared radiation. Everything emits some low-level radiation, and the hotter something is, the more radiation is emitted. The sensor in a motion detector is actually split into two halves. The reason for that is that we are looking to detect motion (change), not average IR levels. The two halves are wired up so that they cancel each other out. If one half sees more or less IR radiation than the other, the output will swing high or low.

PIR Motion 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 sensors input and output. To begin explaining how a basic sensor works, we’ll use this rather nice diagram.

The PIR  Motion 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  Motion 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.

Note that PIRs won’t tell you how many people are around or how close they are to the sensor, the lens is often fixed to a certain sweep and distance (although it can be hacked somewhere) and they are also sometimes set off by house pets.



Most PIR sensors have a 3-pin connection at the side or bottom. One pin will be ground, another will be signal and the last pin will be power. Power is usually up to 5V. Sometimes bigger modules don’t have direct output and instead just operate a relay which case there are ground, power, and the two switch associations. Interfacing PIR with a microcontroller is very easy and simple. The PIR acts as a digital output so all you need to do is listening for the pin to flip high or low. The motion can be detected by checking for a high signal on a single I/O pin. Once the sensor warms up the output will remain low until there is motion, at which time the output will swing high for a couple of seconds, then return low. If motion continues the output will cycle in this manner until the sensors line of sight of still again. The PIR sensor needs a warm-up time with a specific end goal to capacity fittingly. This is because of the settling time included in studying nature’s domain. This could be anyplace from 10-60 seconds.

The Materials needed for the simple PIR project are:

  2. Arduino
  3. Breadboard
  4. Jumper wires (6-10)
  5. Buzzer (if you have set it as output)
  6. LED (if you have set it as output)







This code has been written with output as a buzzer and led and you can change output in this code to servo movement, etc…. too… You have to implement this code by following steps:

Let’s go to some advance project and for that I have given some links which is having interesting projects based on PIR motion sensor. Hold your coffee!, and have some brainstorming after viewing this project, and do some innovation which is invention in itself.

HOW does IT work?