Hi,

 Here's an idea I've come up with in the past few weeks: make a device
that would create a focused, low-intensity ultrasonic field that could
create (hopefully) a "no-cat" zone in front of a computer-monitor for
instance (this is our problem)  The only two problems I see is 1) making
the signal low-level enough that it would just annoy the cat a little and
nothing more, and 2) figuring out how to focus it.  I'm thinking
pizoelectric speakers might be able to do that.

 What is the an *upper* limit on what cats can hear?  The "focusable
speakers" that I've heard of work by using two ultrasonic signals to
create interferance patterns low enough that people can here them (cats
could be a problem here).  Theoretically, the same could be done for
cats, except that the source frequency would have to be higher than the
upper range of the cat's hearing.

 Other than that (which would take quite a bit of stuff, time, money,
math, and experimentation to make), does anyone have any idea how to
teach a cat not to walk back and forth in front of a computer monitor.
Other than having the owner pet the cat rather than use the computer -
which is of course what the cat wants, althogh I think our's does it just
for spite.  We would be perfectly happy if he'd just either sit off to
the side, or lay down, and we'd hapily scratch his head.  But no - he
insists on wandering back and forth in front of the monitor, and
unfortunately, none of us have X-ray vision and the cat is not
transparent :)

Jim