The Touch Probe allows you to quickly identify job zero (X, Y, and Z) by running the probing feature found in Carbide Motion.
Instructions for the Touch Probe can be found here .
The Touch Probe is only supported in Carbide Motion 4 and GRBL 1.1 so you'll need to upgrade prior to ordering. This is only a software and firmware change, no new hardware is required. More information can be found here.