What exactly does an alarm motion censor detect?

Question

There is something strange going on in the old house I inherited. The alarm will go off when no one is inside. Once it was the kitchen, and once in the parlor. There is no way to get past the door and window censors, just to show up in the kitchen or parlor, and trip the alarm. I'm hoping it has something to do with the atmosphere, maybe there is a draft that blows something in front of the censor, although in the parlor there's not anything to move around, we've stripped it bare to start renovations. Or maybe it's a huge rat! Although even a rat big enough to set off one censor wouldn't be able to slink past the others undetected, would it?

Answer 1

found this maybe it will help. sounds like your sensor needs to be calibrated or is pick up some random tempature changes somehow. light from a window or something, heating the floor.



The "motion sensing" feature on most lights (and security systems) is a passive system that detects infrared energy. These sensors are therefore known as PIR (passive infrared) detectors or pyroelectric sensors. In order to make a sensor that can detect a human being, you need to make the sensor sensitive to the temperature of a human body. Humans, having a skin temperature of about 93 degrees F, radiate infrared energy with a wavelength between 9 and 10 micrometers. Therefore, the sensors are typically sensitive in the range of 8 to 12 micrometers.



The devices themselves are simple electronic components not unlike a photosensor. The infrared light bumps electrons off a substrate, and these electrons can be detected and amplified into a signal.



You have probably noticed that your light is sensitive to motion, but not to a person who is standing still. That's because the electronics package attached to the sensor is looking for a fairly rapid change in the amount of infrared energy it is seeing. When a person walks by, the amount of infrared energy in the field of view changes rapidly and is easily detected. You do not want the sensor detecting slower changes, like the sidewalk cooling off at night.

Answer 2

An infrared motion sensor in the kitchen can be triggered by heat from the stove or even from the back of the refrigerator.



Door and window sensors are usually, magnetic. The magnet on a closed door or window closes a switch. This type of sensor is pretty reliable and unlikely to cause false alarms.



Infrared beams shine an invisible spotlight, which reflects off of a corner reflector back to a sensor. Near the limit of their range, you must turn the sensitivity way up. Then they can be triggered by bright lights, like a sunbeam or the reflection of sun from a car windshield coming thru a window.



Maybe your sensor is sonic instead of infrared. Sonic sensors detect echoes at a slightly different pitch (frequency) than that of the source (a little sound transmitter). If the sensitivity setting is too high, it can be set off by a pet, a mouse, a ceiling fan or a moth. Some ultrasonic noise sources, like cicadas outside the house, can trigger such a device.



The best way to avoid false alarms is to tie several sensors into a single computer-controlled alarm system. You could program the system to ignore individual sensors, but sound an alarm when two different kinds of sensors detect something.

Answer 3

Here is one additional explanation. Usually the sensores installed in house detect CHANGE IN THE LIGHT CONTRAST when some person (body) step inside the sensor registerable area (space). Body of this person can smother of the light contrast or amplify him. For example person with black T shirt will smother light contrast, person in white T shirt will amplify it. Integrated circuit into the alarm got registered status (situation) before person is into the sensors registration field (one level of voltage) and after the person step into this field (second voltage). Only if these two voltage are same the alarm will stay passive (out of function). Every changing of second voltage will activate alarm. Therefore you have to adjust all sensors section in alarm on appropriate registration (voltage) level. Veradisca & Best Regards, Neven.

Answer 4

Is there a lot of dust in the air?



Dust + Drafts = Detectable Motion



Window Drafts + Curtains = Motion

(Either the curtains themselves, shadows cast by the curtains or street light let in my the moving curtains.)

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Answer 5

Open up the sensor and you will see the black and white wires and copper ground. Keep the ground and white wires as they are. Now disconnect the black wire from the sensor and wire nut it to the light. Before putting everything back go inside and try the wall switch. If everything works, you can button it up. You could also disconnect and remove the sensor from the light and buy the plug to fill the 1/2" hole at HD/Lowes that was left ,