I was under the impression that security system motion detectors worked on infrared light (could be wrong). Does this mean that either an infrared flashlight would set them off or that they could be defeated by insuring a constant supply of infrared on the detector from an ir flashlight? I'm not planning anything illegal I'm just curious.
infrared flashlights and motion detectors
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WildRice
Flashlight Enthusiast
IR motion detectors use a PIR (passive infra red) device. I am not too how these work, someone correct me if I am worng. the PIR sensor sences far range IR (heat), I also thing the device is temp regulated. I took apart a dead electronic ear thermometer, it was a 4 legged device. Anyhow these PIR devices can detect minute thermal image changes.
Jeff
Jeff
StevieRay
Enlightened
Jeff, you are correct. PIR's are passive. They are composed of mulitple zones within the sensor. They establish a background noise level and look for changes in infrared radiation. The sensitivity on most can be adjusted to look for motion across one or more of the zones before going into alarm. As to whether an infrared light source would be enough to set it off, I don't know. I would supect that it would. I would like to know myself.
Steve
Steve
i7r7
Newly Enlightened
This post reminded me of a time a few years ago (before I started buying all these expensive flashlights) when I was playing around with a dodgy $5 flashlight and a PIR motion detector. I was flashing it directly into the PIR "window" and it didn't detect it (assuming that I didn't move).
A few minutes ago, I tried using my small range of flashlights on an IR sensor (its a USB remote control receiver for my Digital TV card). I'm not sure if it's similar to how a PIR sensor works but its the only IR sensor that I got. Firstly, my SF G2 w/61 shining directly into the sensor didn't make the receiver's LED blink at all... with a deep red/IR filter, same, no IR detected.
However, when I got my Inova X5t, things were completely different. With and without the IR filter, the receiver was able to detect the prescence of IR from the white LEDs. Quite a strong and consistent signal btw...
Conclusion
Whether or not an IR sensor will be able to detect the IR from a flashlight (I'm guessing) would depend on the sensor's wavelength specifications. I'm sure that the SF is emitting massive amounts of IR in the form of heat... but not the right frequency for the IR sensor to detect it.
Jeff
A few minutes ago, I tried using my small range of flashlights on an IR sensor (its a USB remote control receiver for my Digital TV card). I'm not sure if it's similar to how a PIR sensor works but its the only IR sensor that I got. Firstly, my SF G2 w/61 shining directly into the sensor didn't make the receiver's LED blink at all... with a deep red/IR filter, same, no IR detected.
However, when I got my Inova X5t, things were completely different. With and without the IR filter, the receiver was able to detect the prescence of IR from the white LEDs. Quite a strong and consistent signal btw...
Conclusion
Whether or not an IR sensor will be able to detect the IR from a flashlight (I'm guessing) would depend on the sensor's wavelength specifications. I'm sure that the SF is emitting massive amounts of IR in the form of heat... but not the right frequency for the IR sensor to detect it.
Jeff
PIR alarms are designed with circuitry to reduce false alarm problems. While they may see the IR source that doesn't mean It would be intreprited as an alarm. From my experience some pretty weird things can cause false alarms, but flashlights or IR sources haven't been a problem. For one thing read StevieRay's description how they operate. They look across multiple "zones" IR (heat, including body heat) that are stationary should not cause a problem. However I would guess that if you blinded a sensor with an IR source that may be an issue, but I don't know for sure. Also several of commercial motion alarms makers have dual technology, using both microwaves and IR to detect intrusion and reduce false alarms.
GregR
GregR
Harrkev
Enlightened
The PIR is actually a PAIR of detectors which are sensitive to long-wavelength IR. I am not absolutely certain how they are wired, but I do know how the behave...
It appears that the outputs of the two sensors are sent through a differential amplifier. Thus, common-mode noise (ambient temperature change) would not trigger them. Also, the output of the amp appears to go though a large capacitor (high-pass filter). This means that veeeerrrryyyy sssslllloooowww movement of heat from one side to the other will NOT trigger it. The ONLY THING that triggers one of these sensors is heat moving from one side of the sensor to the other at faster than a snail's pace. The lens is a VERY important part of this sensor. Without the lens, it could only determine the ambient temperature. The lens focuses a heat image on the sensor so that movement can be detected.
These sensors usually have multiple lenses in front of them so that they are "multi-directional." Each lens creates its own zone. This is how they can cover a large area. With a single lens, they would be VERY directional.
I would be surprised if they were sensitive to the frequencies used by remote controls. They are supposed to detect IR in the range created by a black-body radiator about the temperature of a human.
It appears that the outputs of the two sensors are sent through a differential amplifier. Thus, common-mode noise (ambient temperature change) would not trigger them. Also, the output of the amp appears to go though a large capacitor (high-pass filter). This means that veeeerrrryyyy sssslllloooowww movement of heat from one side to the other will NOT trigger it. The ONLY THING that triggers one of these sensors is heat moving from one side of the sensor to the other at faster than a snail's pace. The lens is a VERY important part of this sensor. Without the lens, it could only determine the ambient temperature. The lens focuses a heat image on the sensor so that movement can be detected.
These sensors usually have multiple lenses in front of them so that they are "multi-directional." Each lens creates its own zone. This is how they can cover a large area. With a single lens, they would be VERY directional.
I would be surprised if they were sensitive to the frequencies used by remote controls. They are supposed to detect IR in the range created by a black-body radiator about the temperature of a human.
