gpsmikey:
There are load sensing switches designed for that (Rockler.com carries them). You plug it into the outlet, then plug the machine into the gadget. When the machine is turned on, it turns the dust collection system on (could have used that yesterday making a bunch of things for my daughter with a router and template. LOTS of sawdust!!).
Something like this?: http://www.rockler.com/i-socket-110m-tool-and-vacuum-switch
We looked at those, they are great if you have 2-3 machines max and then it starts getting expensive. They also don't work very well with a central dust collection system like we have.
The shop is a large 2 car garage that has 7 machines (and growing) spread out all over the garage that are all piped to a central dust collection system. We also want to automate the blast gates after we get the auto run up and running.