On 24 Dec 2005 23:22:30 -0800, miso@sushi.com wrote:

You can read about the sensors here:
http://web.archive.org/web/20031227062056/www.qual-tron.com/page9.html
http://www.sandia.gov/isrc/perimeterdetection.html

Once the story about the sensors hit the press, Qual-Tron removed much
of the information on their products from the net. Fortunately, it was
archived.

Not shown here, but there are three versions of the magnetic sensor
based on sensitivity. Generally, you are talking about detecting a car
at 30ft. Place them carefully around the "intersections", and you can
figure out direction of travel by the sequence in which they are
tripped.

EMIDS and MIDS are coded, so you can't simply fire up a carrier and
expect the receiver to think a sensor was tripped.

It is rumored that there are amonia sniffers for EMIDS applications,
with the intent to sniff a person walking by them. Eh, maybe.....

             Did I see something once about geophones ? I may be way out
of date here but I tthought that geophones were more for walking people
type targets rather than vehicles. As an example: The Brits used to keep
them around Stonehenge for the odd (literally) Druid that might show up in
the middle of the night.

                     Andrew