Ask Mad Physics: Police Jammers (printer friendly)

Question: If a cop uses IR to check your speed, couldn't you just use a simple remote control to jam his signal? - Gant

Answer: Short answer… no. The first and most practical reason is that remote controls are relatively weak and they don’t have a great range.

Furthermore when we talk about remotes they would have to be 500 times brighter than the 25 milliWatts the police tracks you with to beat the retroreflective. Also seeing that remotes have short ranges, you may be out of luck because at shorter range, the problem of jamming is worse. The police LIDAR (laser radar) power grows as the range decreases, and your jammer’s power grows exponentially slower. The reason jamming is not feasible is that you have to broadcast into all directions, reducing the power aimed at the LIDAR gun. So that is the disappointing answer, but instead of leaving you with that, we thought we’d propose less intelligent solutions! Clearly you could go out and buy jammers and other such tools, but why not create our contraption:

The Fog of Deception!

WARNING: This is not serious, we would never recommend this to anyone. We just chose the worst possible solution so we could use some physics. This is illegal and dangerous!

We did some research into the police LIDAR. The acronym stands for light detection and ranging or laser imaging detection and ranging and it is a technology that determines distance to an object or surface using pulsing lasers. These lasers have a very high resolution, and we can exploit that weakness.

LIDAR is used commonly in meteorology because it is very sensitive to fog, clouds, and aerosols. This means if we can just track police cars (with scanners) we can block the signal with some sort of diffusion of particles.

We could use spray aerosol, but that would get the car dirty. Instead we can generate smoke! Here’s how we did it:

Instead of using a fog machine we strapped a small rocket motor to the back of the car. We tethered it to a gunpowder igniter and strapped it to some wires. Then once a police car shows up we connect the circuit to the 12V battery and ta-da! The LIDAR can’t see the car, and the police can’t see the license.

Look at the video below to see our prototypes in action.

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Cite Our Experiments & Research

If you have used any of this information or any of these images please go ahead and cite them in your bibliography. For your convenience, this is what the citation would look like in MLA format:

Family, Afrooz. “Police Jammers .” 31 May 2005 Mad Physics. dd mmm. yyyy ^†

<http://www.madphysics.com/ask/lidar/>

We are glad to share our knowledge with you as long as you cite all of our info, and contact us before you use anything for non-educational purposes (commercial, etc.).

† In the bibliography you must insert the day you visited the site (this is relevant because the site could change at some point), therefore, in the bibliography above replace dd with the day you visited, mmm with the abreviated month, and yyyy with the year (ex: dd mmm. yyyy becomes 23 Dec. 2004).

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