> LOUD alarm if anybody tries to "Borrow" it without my permission. It will
> have a small keypad to arm/dis-arm it and must be about the size if a
> ciggarett packet. it will run of a 9V battery. I have most of the keypad
> and I/P O/P code sorted so far it's based on a 16c84. So if anybody has any
> ideas on motion dectection please let me know. It dosent have to be linear
> just digital will do. IE motion /no motion but the sensivtivity must be
> quite good.
>

Try this:

Take two concave glas circles. (Used in chem labs, don't know the
fancy name). I used ones about 1" in diamiter. Put a drop or two
of mercury on one and cover it with the other.

Now you have a conductive liquid runing around in an enclosed space.
Now you slip a couple of dozen contacts inbetween the two edges and
glue everything shut. As this gets bumped and tilted it makes and
breaks contacts like mad.

I read this with a PC where I  could dedicate 32 lines, but there
must be an trick with resistors and A-D's that lets you get away with
less. Or just put in only say 12 wires. Hook them up alternatly to
+ , input , gnd, input. Gives you six I/O's used and probably more
than enough sensitivity. Keep scanning the pins and when it moves
the bitpattern will change.

Nic