If money wasn't an issue, you could fairly easily implement a
scanning laser and detect changes in the environment.  See:
http://www.helpmaterobotics.com/RC_components/RC_lightranger.htm

        The ideal inexpensive human detector is a pyroelectric sensor,
Eltec has some nice units and some arrays that might be useful.  The
thing to remember about pyroelectric sensors is that they only detect
changes in temperature.  I think a couple of the pyroelectric arrays
combined with a lens would also work pretty well with a minimum of
processing overhead.  Not sure about the range issue though.

Ben



        ----------
        From:   Bertel Schmitt[SMTP:bschmitt@PANIX.COM]
        Reply To:       pic microcontroller discussion list
        Sent:   Tuesday, January 20, 1998 5:58 AM
        To:     PICLIST@MITVMA.MIT.EDU
        Subject:        (OT) Laser or ???? ranging

        I'm working on a security application that detects a moving
object (usually
        a human  ...) in an outdoor space measuring approx 200 x 500 ft.
Output are
        x/y (maybe even z) coordinates, which are fed to a  x/y/z- mount
with a
        video camera on it. Mount gets coordinates, aims, zooms in,
focuses -
        smile!. Video camera and x/y/z mount are done. All I need is the
ranging
        module. Ultrasound is out of the picture because of the
distances involved.
        Motion detectors etc. don't work, because I need the exact
location of the
        object, not just presence detection.

        Any ideas?