PIR motion sensor and open window

[lleo]

Well, it is summer and nice outside.
I finally caved in to pressures to close all windows before leaving the house and arm the system.
Before I change things on the programming side, it occured to me if the indoor motion sensors would be tripped by movement outside?
The window would be open with a screen on. I know that PIR does not cross glass, but what about bug screens?
 

 

[ano]

No, that shouldn't be a problem if they are passive IR sensors, which most are. They aren't just detecting motion, they are detecting motion of objects that give off heat. If non-living things move, it is quite rare they will be detected. I don't want to say "never" because if the object is hot it could trigger it, but certainly moving papers of the same temp as the background won't. Also, passive IR detectors measure motion only in certain directors across the sensor, and usually only horizontal. Motion moving toward or away from the sensor is ignored. (Unless its a microwave or ultrasonic sensor, but its not likely you are using those.) So all-in-all, it shouldn't be a problem.

 

[lleo]

Thanks for your reply. I did a casual walk test and indeed did not pick up motion. I know that motions should not be pointed directly to windows, but in many areas there is just no other way, but to include the window in the field of view of the PIR. Today it was 85 or so, maybe the temperature differential was not big enough.
Conceptually, I think it should pick up movements, just as the screen does not block view, it should not block light or heat signature, this is why I am asking here...
 
Separately I have an occupancy sensor which "sees" through a open door frame, and walking in the adjacent room results in turning the lights on. I also think heard somewhere that occupancy sensors and PIR motion sensors are different and have different logic for activation, so maybe someone passing in front of window will not set the alarm off, or at least I hope.

 

[Del91574]

Not recommended.
 
PIR's have a variety of ways they work, but you can't make a blanket statement that they won't see movement away or towards the detector unless the optics and lens are considered OR if there's a mirror involved with the PIR...I know of a lot of units that have mirrors involved. It doesn't make a difference what temperature the background OR item within view of the detector are....the detector doesn't care, nor can it judge temperature, it's only looking at contrast between a background IR and a sharp contrast with movement across the pattern (again, maybe segments, may be small "dot" targets within the FOV-as the case with fresnel lens units). In the case of "non-living things" setting off PIR's I've seen almost all of them and it does happen. If it moves, it can set off the detector.
 
The issue is going to be the inability to control what is within the field of view. It may be fine, but a good enough breeze or other item that is within range of the detector....well all bets are off.

 

[Del91574]

Not recommended.
 
PIR's have a variety of ways they work, but you can't make a blanket statement that they won't see movement away or towards the detector unless the optics and lens are considered OR if there's a mirror involved with the PIR...I know of a lot of units that have mirrors involved. It doesn't make a difference what temperature the background OR item within view of the detector are....the detector doesn't care, nor can it judge temperature, it's only looking at contrast between a background IR and a sharp contrast with movement across the pattern (again, maybe segments, may be small "dot" targets within the FOV-as the case with fresnel lens units). In the case of "non-living things" setting off PIR's I've seen almost all of them and it does happen. If it moves, it can set off the detector.
 
The issue is going to be the inability to control what is within the field of view. It may be fine, but a good enough breeze or other item that is within range of the detector....well all bets are off.