I've been developing an automatic toolsetting device for our own use in house and it works great and I'm ramping up to sell it.

Here are the particulars:
-self contained black box micro-computer driven and battery powered with a db-25 rs-232 connector on it
-interfaces with the rs-232 port of your CNC machine in DNC mode

How it works:
-has a bunch of dip switches, one for each tool you want to zero
-has a capacitance switch on the unit. when the metal part touches the top, the capacitance changes and this is detected
-uses DNC drip feed mode and sends a Z down command to the CNC controller through DNC mode then checks the sensor, if it hasn't hit yet, it issues another Z down command keeps going down until it touches
-once it touches, it tells the CNC controller to write the proper offset into memory, taking into account the thickness of the device (so offset 0 is your table 0)
-issues a tool change command until it cycles through all your tools

Benefits:
-no retrofit necessary
-no manually entering offsets, fully automatic
-uses standard G-code commands over RS-232 DNC drip feed mode
-inexpensive: right now pricing is set for $150 for 1 tool, $250 for up to 5 tools, $500 for 20 tools, $1000 for up to 100 tools

Right now I have configured for a Haas machine but any standard g-code can be programmed in the unit here.

Pics to follow soon.

PM me if you are interested and want to be kept updated/want to beta test.