Laser based speed detectors?

[Yossarian451]

This is mostly inspired by the multitude of "Radar Detectors" which claim to be able to spot laser dectors. I am wondering the phyics of that one, becuase the very concept is that you can't really dectect a laser, as it is a beam of high intensity and single band light.

My understanding of the systems that the police use is that it simply shotts multiple times and checks the change in distance. It is very fast and of course happens at the speed of light. NOw how can you "detect" this. Lasers are directional, unlike the actual radar which just sends out an electromagnetic wave and then picks it up again. That all makes sense, you just sniff the waves out and you can easily detect if one is in use, you can even jam them by sending out the pulse yourself and all it reads is infinately high speed.

Back to my question, I guess I am asking is it a sham what they claim, or is it real and how.

 

[silverpig]

The detector can tell if it's being hit by laser radiation. Of course this won't help much as the cop will already have a reading. There is a device which, once it has detected a laser, will send out pulses in that frequency range to "confuse" the cop's laser gun, giving you time to slow down before he gets a good reading.

 

[Yossarian451]

So what is the width which the laser hits with, because I have serious doubts about those things. It seem more like a sham, and an easy claim for these makers to say but I don't really believe it. It would have to small a range to be reliable.

And the latter which you describe would be probably classifed as a jaming device which is illegal.

 

[Akira13]

My detector has an "eye" on the top, away from the main sensor array. The instruction manual said that the eye is bi-directional, and looks forward and backward (so it should be placed such that it has a clear view of the front and back windshields).

A laser has some dispursion, so it is not a single point of light. At a fair distance, you can get a laser to be the size of a manhole cover.

It is very easy to detect laser light using a photodiode or phototransistor. I'm sure there are other good ways as well.

 

[Pulsar]

A laser detector detects the scatter from the laser when it hits an object around you. The scatter, however, on a laser is much much lower than that of a directional radar, which means that you get FAR less warning, and will probably see the cop before your detector does you any good.

 

[Mday]

highway mounted laser detectors transmit their readings wirelessly via some radio frequency. this frequency or set of frequencies are known. what many "laser detectors" do is detect those radio frequencies. so, a laser detector is just a radar detector. of course if a cop is holding the speed detector... the transmission is obviously the screen of the machine he's using.

as for actual laser detectors, what they said.

 

[gsellis]

Also remember that the lasers are a specific freq., so the detector only has to look for changes in certain wavelengths. That makes it easier.

 

[RussianSoldier]

if you're friends with any local cops, see if you can't test it out...

 

[silverpig]

Originally posted by: Yossarian451
So what is the width which the laser hits with, because I have serious doubts about those things. It seem more like a sham, and an easy claim for these makers to say but I don't really believe it. It would have to small a range to be reliable.

And the latter which you describe would be probably classifed as a jaming device which is illegal.

No, it's not illegal. Google it and read about it on their website. I found the post here I think quite a while back.

 

[vegetation]

Originally posted by: silverpig

Originally posted by: Yossarian451
So what is the width which the laser hits with, because I have serious doubts about those things. It seem more like a sham, and an easy claim for these makers to say but I don't really believe it. It would have to small a range to be reliable.

And the latter which you describe would be probably classifed as a jaming device which is illegal.

No, it's not illegal. Google it and read about it on their website. I found the post here I think quite a while back.

It certainly is not illegal. In fact, the FCC does not even govern the use of laser spreads. The FDA does. The manufacturers only have to make sure there is no potential eye damage.

 

[JediJeb]

Originally posted by: vegetation

Originally posted by: silverpig

Originally posted by: Yossarian451
So what is the width which the laser hits with, because I have serious doubts about those things. It seem more like a sham, and an easy claim for these makers to say but I don't really believe it. It would have to small a range to be reliable.

And the latter which you describe would be probably classifed as a jaming device which is illegal.

No, it's not illegal. Google it and read about it on their website. I found the post here I think quite a while back.

It certainly is not illegal. In fact, the FCC does not even govern the use of laser spreads. The FDA does. The manufacturers only have to make sure there is no potential eye damage.

Correct the laser jammer is not illegal, but the microwave jammer used to jam traditional microwave based detectors is illegal because you would be required to have an FCC liscense to use it.

 

[IHYLN]

Originally posted by: Yossarian451
So what is the width which the laser hits with, because I have serious doubts about those things. It seem more like a sham, and an easy claim for these makers to say but I don't really believe it. It would have to small a range to be reliable.

And the latter which you describe would be probably classifed as a jaming device which is illegal.

you can't regulate light, otherwise you would need a license just to have a flashlight

 

[JediJeb]

Originally posted by: IHYLN

Originally posted by: Yossarian451
So what is the width which the laser hits with, because I have serious doubts about those things. It seem more like a sham, and an easy claim for these makers to say but I don't really believe it. It would have to small a range to be reliable.

And the latter which you describe would be probably classifed as a jaming device which is illegal.

you can't regulate light, otherwise you would need a license just to have a flashlight

Uh well actually they do regulate light. Over a certain Joule rating lasers have to be liscensed.

 

[JediJeb]

Doh, DP

 

[dnoyeb]

I have only ever seen lasers use against the flow of traffic. This means the aim is more down the road, and gives you a better chance of picking up someone else getting gunned.

My rule is to never be past 5MPH over, and be out in front of trafic. Be very careful when you are the leader, laser or no.

 

If I remember correctly, the laser is only about 5 feet wide at 1000 feet. Most of the time, by the time you have a change to know whats going on, the cop already got you.