After paying a rather large amount to keep my car in a car park with a ticket to get out. Should of taken the caterham and driven under barrier

To get in you have to drive up to a barrier and push a button and it gives you a ticket to let you in

To stop you getting a ticket with no car there is some sort of loop in the ground to detect said car.

Is it possible to build a pocket sized device to stick near this loop to pretend to be said car ?

I don't know about pocket sized, but I hear a dustbin lid works well. A metal one that is....

yeah but you can hardly keep a dustbin lid in the boot

But on a side thought there is a type of speed camera that works with two of those loops in the road.

Now imagine the fun you could have if you could set those off at will while sat in a wheel barrow, office chair, bathtub in front of the camera.

Now imagine the fun you could have if you could set those off at will while sat in a wheel barrow, office chair, bathtub in front of the camera.

That is a very funny thought. If the police wern't already looking for me for some other unpaid fines I'd do it just for the picture.

Just one question however....What is a dustbin lid? Is it just a flat peice of metal like i have pictured in my head?

get your self a steel wire cable about 30 to 35 feet long.
create a loop about 1and 1/2 feet in diameter by coiling the cable several times and leave a good 15 feet. (or however long you need it to reach plus a few feet so that you can throw it just passed the sensor)
You can use duct tape to hold every thing together.
Now just toss your device just passed the sensor and drag the loop over it.
Ahh, access.

That loop is a magnetic sensor that detects when a high permeability material passes over the loop because of the inductance change of the loop. Kinda like an electromagent.

These things are also used (in the US at least) to trip on-demand traffic lights, especially turning-lane lights. This is a huge problem for motorcyclists because most bikes are mostly aluminum and don't have enough ferrous metal to trip the sensor.

One enterprising fellow is selling a relatively small (but powerful) magnet that will trip the sensor. Magnets are much higher permeability than steel, even, so a relatively small magnet will work. Small enough to carry around.

The only problem is -- it's a magnet! I don't know many computer people who want to lug around magnets. On the other hand, I think the empeg is pretty well shielded, and most people use optical media now, so... you might want to try it:

Green Light Trigger

Jim

more info here:
http://auto.howstuffworks.com/question234.htm
and
http://www.greenlightstuff.com/