I worked for a company a few years ago that used spring loaded probes that could be placed in the spindle. They would "kick off" when the edge of the probe was touched on the work surface, be it fixture, work piece etc.

It was perfect for setting up work offsets (G10s) and I imagine a damn sight cheaper than purchasing a light probe of some kind.

Trouble is I cannot find anywhere to buy them. I am unsure of their product name so I cannot find anything online. They come in different types from ball, needle, long, short.

Failing that I am interested in what others are using, obviously in the milling field.