General Question

riskyBusiness's avatar

How does police LASER speed detection work?

Asked by riskyBusiness (83 points ) August 3rd, 2009

How does police Laser speed detection work, and how do Radar/Laser detectors work regarding how they detect it?

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11 Answers

Ivan's avatar

Doppler

MrGV's avatar

Radar reads the frequency around your car.
Laser measures the reflection time.

Ivan's avatar

@MrGeneVan huh?

The RADAR gun emits a laser of a known frequency. Because your car is moving, the reflection of this laser has a different frequency. By measuring the frequency change, and knowing the speed of sound and the speed that the RADAR gun itself is traveling at, the speed of your car can be calculated.

Zendo's avatar

However, the device must be properly calibrated, and speeding tickets are often beat in court due to lack of said calibration!

kfingerman's avatar

Think of it this way. A light/sound/radar wave is like this: /’’\../’’\../’’\..Frequency is the time between the peaks in a wave. Say the time between peaks is 1 second (not real, just for the ease talking about it). If the detector is emitting a wave that has that 1sec frequency and that wave is bouncing off a stationary object, then each of those peaks would bounce off 1sec apart it would come back at the same frequency. If the object is moving away, then each of those peaks would have a bit farther to go than the one before it, meaning that 1sec gets stretched out. Opposite is true if the object is coming towards the detector. Does this make sense? This is why a car that is coming towards us sounds high pitched and then suddenly switches to low pitch as it passes. It makes only one sound, but the waves are being compressed coming in and then stretched going out.

Deepness's avatar

@Zendo Not in NYC. It is so so so tough to beat a speeding ticket here.

Noel_S_Leitmotiv's avatar

Other answer:

Police departments want more revenue.

john65pennington's avatar

Lasar radar works like this: lasar radar only works on one vehicle at a time. the unit first has to be calibrated by the operating officer. lasar radar emits two lasar beams. one to reach the target and one to return to the lasar unit. the lasar beams have many frequencies, which constantly change. in other words, radar dectectors are of no use in lasar radar. the officer believes a vehicle is speeding. he aims the lasar radar unit at the rear of this one vehicle. instantly, the results are calculated within the unit and a reading is posted on a screen, thats within the lasar unit and displayed to the officer. this action is split-second and 100% accurate. lasar radar has been challenged all the way to the U.S. Supreme Court and has never lost a case. an no, the officer is not required, by law, to show you the lasar radar results of your speed at the time of the stop. lasar radar workd entirely different than regular doppler radar. lasar radar is much faster and much more accurate.

gorillapaws's avatar

@john65pennington so if there are several cars in a pack, that’s somewhat far away, how does the officer know which car he’s getting the reading from? I guess if all of the vehicles are traveling about the same speed it wouldn’t matter much, and if one is going faster than the others that would be the one you pull over, but is there a way to verify what you’re aiming at (since you’re shooting invisible beams with no visual feedback)?

SecondHandStoke's avatar

LASER works by sending a light signal to the target instead of microwaves.

From the Valentine One website (by FAR the most comprehensive RADAR and LASER receiver available):

http://www.valentine1.com/v1info/laserdefense.asp

The pencil thin beam used by LASER requires that the officer hold the device DEAD STILL.

It’s arguable that issuing a deserved speeding citation using LASER is much more difficult.

@gorillapaws LASER devices do provide visual feedback to the fascist pig, I mean officer.

Note that a quick reaction to a LASER warning is vital.

It should also be noted that in the operation manual for many speed detection devices there is a disclaimer that states in so many words that the product is not recommended for vehicle speed detection.

Do your homework before contesting a citation in court.

All while Germany has sophisticated equipment that measures a FAR more important aspect of safe driving:

Proper space between vehicles fore and aft. Ugh…

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