motion detectors

[Ice_Phoenix87]

how do motion detectors work? i want to set up some for my shed, i was told little kids can get past them. any ideas thanx

[YT2095]

there`s about 5 different types I know of (and variations of each), what had you got in mind in particular?

[Ice_Phoenix87]

i dunno, whats the best or lest expensive are they easy to get past?? maybe i should just have landmines outside the door for security

[ydoaPs]

don't they use lasers and timers as a sort of radar?

[drz]

My friends neighbors have a motion activated flood light. When I drive by, I set it off, unless I move quickly. We also have sensors on our auto doors at work that have to be adjusted every so often for sensitivity. Somehow they even have sensors that only respond to metal objects of a certain size. (BTW, can someone explain how this works? A metal can for instance, doesn't open the door, but something like a small cart will??)

 

Anyhow, depending on what you want to do, a simply flood light would probably do the trick. You could go a step further, using the flood light, figure out someway to tap into the power, run it to a buzzer or something.

 

a couple links google spit out:

 

http://www.smarthome.com/outdoormotion.html

http://www.safetycentral.com/homandbusals.html

[Ice_Phoenix87]

i was told someone in one of those heat blankets, the silver ones can get past the motion detectors, is this correct?

[ydoaPs]

I don't know about motion detectors, but they shut off ELTs.

[5614]

i may be wrong, but here's a guess anyway;

 

maybe they send out sum kinda waves, not light, anything else, and it 'gets used' to what it 'sees' and then, when there is a change it set off the circuit, by closing a switch, or some such, this is why, if you walk past it, you are changing the image it sees, by making the waves return quicker, than originally, when you move the detector itself what it 'sees' changes, but if you move quickly, then the image moves to close for the detector to register.

 

apparently if you drive at i think about 120MPH in the UK then you are going too fast for the speed cameras to pick you up, but no garentees, i heard it on the news or sumin, it might not be reliable and accurate data!

[ydoaPs]

that was wat i was thinking.

 

DON'T DO IT! your government is trying to trap you. they want you to speed.

[Sayonara]

apparently if you drive at i think about 120MPH in the UK then you are going too fast for the speed cameras to pick you up, but no garentees, i heard it on the news or sumin, it might not be reliable and accurate data!

That's not true.

 

However if people want to try it, I say let them. It will get some of the idiots off the roads.

[5614]

ok, fine just passing on something i heard, my mistake.

 

i'll take your word for it! and to be honest i had no intention of driving at 120MPH maybe its a tad on the fast side,

 

at the same time, there must be a speed where you can dodge the cameras, the area they "scan" is not very long, just a thougth [with no backing what-so-ever!]

[ydoaPs]

I know, shoot the camera then drive as fast as you want.

[Ice_Phoenix87]

hmmm, glass should get past infrared

[YT2095]

PIR detectors can be "fooled" easily, as can speed cams.

why not use a pressure mat or a break beam detector?

 

you have to factor in that it`s a shed and there will be many false alarms when using PIRs, MWD, USD, seismics etc...

 

such things as break beam or pressure mats aren`t likely to give false alarms in that environment though

[RICHARDBATTY]

Pasive infrared sensors have an infrared sensing component. The lense on the front focuses the ambient heat from segments of the surounding area like the blades of a chinese fan onto the sensor. At start up a timer allows the value of ambient heat to be set then switches the circuit to comparator mode. The preset value is allowed to vary slowly but abrupt changes vary faster than the preset can and a relay switches on. The lense gives a pulse effect as a heat source passes each segment and this can be used to prevent false triggers by counting the number of pulses in a given time. A pir that gives you the option of selecting the number of pulses before triggering will be best as you could set it to five and place it at right angles to the door. Only someone passing five segments in a row will trigger the pir but at close range that will only be a step. If you can put it in this position you will only need a narrow angle. The wider angle one may be more expensive. Also bear in mind that some use solid state relays and require a minimum wattage load like the 500 watt bulb they normaly operate. If you plan on wiring something else to it other than the bulb you may need to put another load in parallel to get up to the required power. If the load you are using is higher you will have to set up a seperate relay in parallel to operate the load. Trying to sheild your heat will probably make the area your in lower than ambient and still trigger the sensor. The only way round a decent pir is to move so slow that the change doesn't register as it is within normal allowed ambient temp rise rate. This is so slow it wouldn't be worth the effort.

[Douglas]

how do motion detectors work? i want to set up some for my shed, i was told little kids can get past them. any ideas thanx

I have infra red detectors inside my house (they sense the heat from your body) they're expensive and run off batteries that last about 1 year. If they're set up right, they're foolproof, no kid can get past them, unless they enter the house with 8 inches of insulation wrapped around them.

 

I think my outdoor motion detectors work like doppler radar (similar to what the police use for speeders (motion)). they're cheap (not the police one's). They have a light sensor so they don't work in the day, that can be defeated by placing elecrical tape over the sensor. But, the problem with these, is that the leaves rustling in the trees can set them off. These detectors have a sensitivity adjustment (the infra red don't). A kid might be able walk up to your shed if he/she is walking very very slow.

 

They also have the light transmitter/receiver type, similar to the garage door type. Not sure of the price. They're the photon detector type. You put the light transmitter at point "A" and the receiver at point "B", if the light beam is broken, a hand grenade go off.

 

On second thought, your land mine idea is probably the best. How many kids in your neighborhood ?

[Guest kalimullah k]

i dunno, whats the best or lest expensive are they easy to get past?? maybe i should just have landmines outside the door for security

hi

i think that best way to detect the motion of any thing through infra red sensors

thanks

[5614]

but then it will only detect living things, a simple device can block the heat from reaching the sensor as you run across past it (such as a cold metal block across the sensor... also it will not work for non living things such as a long handed pair of tweezers (or something like that) which could pick up the guarded item (assuming it is of the right size) and thus bypass the security... something which sends out its own waves and can check when the "echo" of the waves changes would be far more efficient.