Passive Infrared Sensors

Webster would tell you a passive infrared sensor is an electronic device which measures infrared light radiation from objects in its field of view. I’ll just tell you it’s the best way to notice an intruder in the dark and the fact that it’s basically a motion detector that is designed to notice temperature changes. Say if a warm bodied human passes in front of a wall, you would have a clear image of that person and of what they are doing. The reason why they call it a “passive” infrared sensor is because the PIR as it is called, doesn’t emit energy of any type instead accepting incoming infrared radiation.

It detects a difference in temperature between people and objects that have a surface difference in temperature of at least +/- 2* C. Plus it has to happen inside of a zone and have a moving rate of 10cm per second. And yes, both temperature and movement is required for this thing to work. But you have to be wise like an owl when you choose the location of the sensor. If an intruder is smart enough, or does his/her “homework” before violating your privacy, he/she would be able to get around any detection zone and make an entrance elsewhere. Location, location, location!! Besides that, I'm sure it wouldn’t hurt to take other measures in home security, some of which you may read about in other articles I've written.

PIR’s are the most common sensors used in today’s market. They have proven themselves too useful and effective. Most PIR’s are not sensitive to things such as radio signals, wind blown debris, or weather such as rain, snow, thunder, or lightning. I'm not sure about earthquakes or hurricanes or tornados, those weather patterns could very well destroy everything including the sensor. The main thing these things run off is heat.