How to detect presence of humans inside a room???

I am thinking about making a project where the the lights/fans ad other electrical appliances in a room are switched off the moment no one is present inside the room.
I am thinking about using a PIR sensor to detect when a person enters a room. But the problem is that PIR sensor detects a change in heat. If a body with heat much more or less passes infront of it, only then it gives high output. But in my project, a lot of people may be inside the room for a long time. So the reference heat as sensed by the PIR sensor is that of human body. So if a person sits infront of the sensor, the sensor will think that since there is no movement, there is nobody inside the room. So it will shut off electricity.

So can anyone provide any ideas about how I can make my system fool proof?
I can use a combination of sensors. It is not necessary to use only PIR sensor. The only thing is that the system should be foolproof. There should be a way to detect the presence of humans inside the room

i think use motion sensor .

You could use voice recognition to detect the occupant(s) yelling "hey, turn the fucking lights back on!". ;-)

But seriously, how about multiple PIR sensors, possibly coupled with some ultrasonic sensors. I seem to
recall there being a thread about this topic fairly recently, and the term "occupancy sensor" came up.
That might be a good starting point.

Good luck with your project.

hi,
That is the nice project. The PIR sensor detect the heat of radiation.its OK. If The person is sitting in front of the PIR, there is no Movement. So the PIR detects the radiation,but We can make it as a b OFF condition. We can adjust the threshold value in Software. We can Set the Upper and Lower Limit in program . you say The group of people inside the room.So it is a big Hall. You can use Some more PIR sensor in different Places. this project will be used in Big offices.

Good luck for your project.

such sensors should be readily available..I have seen these kinds of sensors in UK.

such sensors should be readily available..I have seen these kinds of sensors in UK.

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Yes, these sensors are just regular PIR motion sensors. The original poster has expressed some doubts, if they work for a person sitting in front of the sensor. I expect, they will.

You should learn about the operation details and do some tests on your own. Basically the sensors are sensitive to temperature changes only, but they have multiple zones (depending on the design of the fresnel lens mounted in front of the PIR sensor). If you slightly move your arm, the sensor is able to detect it.

If you are testing the sensor in an office with slowly performing civil servants, there may be a problem.

if they work for a person sitting in front of the sensor. I expect, they will

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I observed that the sensor was mounted in one corner of the room at the top looking down diagonally, with this position it was able to detect even the slightest motion, but I wonder why any normal person would sit like a statue for long hours.

Another option is a software based one, connect a webcam to a PC, a software to capture images from the webcam would have to be developed, the image would then have to be compared with previous images to detect any changes..

This sounds complicated but few years ago I developed an application in Microsoft Visual Basic that did this, I used some proprietary activeX control that did all the image processing, capture and image comparison and generation of events, I think you would have to look in the internet for this..at that time it was a shareware...

thanks
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I wonder why any normal person would sit like a statue for long hours

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A joke tells: "Two civil servants found their colleague sleeping on his desk, when they asked him to join their lunch. - He said, no thanks, I'm working through this lunchtime."

:-D:-D:-D

That is funny..