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cdg

Aug 29, 2017
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my house was broken into
we found that the alarm motion sensor was installed upside down
is this responsible for for no alarm going off
 

ChosunOne

Jun 20, 2010
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Jun 20, 2010
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Probably, yes, assuming that your motion is like 99+% of the motion sensors installed in homes.

The coverage of most (properly installed) motion sensors is "out-and-down", i.e., anywhere from 25 to 40 ft out from the sensor, in a fan pattern, and down. Most motions are designed to be mounted on a wall/corner about 7-7.5 feet high, and don't cover anything higher: If you have a 12 ft. ceiling with a heat register, for instance, the motion won't see it.

Motion sensors are sometimes deliberately installed upside down but 4 feet above the floor, to avoid seeing pets but still catch walking humans. Installed upside down, they see out and up, and ignore anything lower than their position.
This sometimes works with pets that can't/don't climb on furniture or jump at insects inside the house.
 

Bluejets

Oct 5, 2014
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Typical PIR sensor zone arrangement.

Used a 2 bob installer eh?
 

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kellys_eye

Jun 25, 2010
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It would depend on the situation and the orientation of the sensor. It doesn't 'not work' if installed upside down - as other posts show, the detection pattern is still capable of covering an area - however inadequately - regardless of its orientation so making a specific statement that 'incorrect installation' is (perhaps) the 'sole' reason the system failed to detect intruders couldn't be positively proven in, say, a court case.

It may well be a contributory factor but not the sole cause.

But surely the system was tested after installation? If the detector was so badly installed as to fail to detect intruders it would similarly have failed during the commissioning procedure???
 

ChosunOne

Jun 20, 2010
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It would depend on the situation and the orientation of the sensor. It doesn't 'not work' if installed upside down - as other posts show, the detection pattern is still capable of covering an area - however inadequately - regardless of its orientation so making a specific statement that 'incorrect installation' is (perhaps) the 'sole' reason the system failed to detect intruders couldn't be positively proven in, say, a court case.

It may well be a contributory factor but not the sole cause.

But surely the system was tested after installation? If the detector was so badly installed as to fail to detect intruders it would similarly have failed during the commissioning procedure???

@kellys_eye, I'm a senior alarm technician (I believe they may be called "field engineers" in the UK?) here in the USA, specifically in the Washington DC area, which includes Maryland (MD) and Virginal (VA) suburbs for at least 50 miles out. I've also installed and serviced alarm systems in New Jersey (NJ) and New York (NY). Beyond that, for the last 8 years or so I've volunteered my time on various DIY forums like this one, but specifically for alarm systems. So I'm pretty sure about the advice I'm giving here as it applies to North American alarm systems.

I DON'T know everything there is to know about alarm systems, but I'm pretty confident about what I do know.

I know that there are significant differences between the way alarm systems are designed. configured, and installed in North America and the UK and Europe; both in the equipment and in the wiring configurations. Aside from the technical differences, there may also be differences in government regulation standards they have to meet. For that reason, I limit the advice I give to DIY-ers overseas.

Here in North America, the alarm industry is largely unregulated. In my particular area, technicians are required to be licensed (in MD) or registered (in VA), which required background checks and a certain rudimentary course in technical details that strive to limit false alarms---but there are virtually no required government standards that alarm systems have to meet as far as actually detecting intruders.

There is no government regulation about testing a newly installed system before "commissioning" it. Any respectable alarm dealer with require its installers to test a new system, of course, but there is no actual legal requirement to test it, in any county or state that I'm aware of. There is no standardized "commissioning procedure."

To reiterate: If the motion sensor is a normal PIR or "dual-tech" sensor (PIR and MicroWave combined) and was installed at a height of about 7 feet, and was installed upside down---no, it WON'T detect bodies moving about below 7 feet, and the farther out from the sensor, the greater the height below which it won't detect motion. See the coverage diagram that Bluejets posted. That's a generic PIR coverage pattern.

IF the OP's PIR was installed improperly--and we don't yet have the information to know that---then he might have recourse to sue the installing company for his for any loss. Again, probably a major difference between the USA and UK, lawsuits here often depend on what part of the country we're in, state and county or city.
 
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