You might want to look at something like a "Enabling Switch"
http://ab.rockwellautomation.com/Pus...ing-Switches#/
These are commonly used in Industrial Robot Cells. They are a 3 position switch: Open = Disable, Middle Position = Enable, Closed (all the way) = Disable. If you close the switch all the way you have to go back to open before it will enable again.
We have used this as a wired (2009 Driver Station) and wireless e-stop for our robot. The problem with the wireless version that we made is that we have to simulate the "Enter Key" for disable and "F1" for enable. It just isn't that reliable because we have to repeatedly send the "Enter" key and it will freeze up some computers.
This issues we had are from our implementation of the switch. If this is going to be directly on the robot, I would recommend that you electrically control the motors/disable function and NOT rely on software for a safety issue.
Hope this helps,
-Clinton-