X11 Kill Switch

I think it'd be very handy to have a small usb button that when tapped kills the currently focused program in X11 and when held down restarts X11 all together. This'd remove the annoyance of having some bad program grabbing control of the keyboard and mouse and then proceeding to die, effectively rendering the computer unusable. Being a semi-decent operating system you can of course rescue things by logging in via SSH and killing the offending program but this requires a spare computer on the same network, the ability to just quickly click a button would be much nicer.