A printer is essentially a sophisticated plotting machine that moves to certain coordinates told to it by the slicer in the programming language G-code. That's why slicer software is so important.

When a print job is finished, custom G-code causes an attachment on the printer to wedge itself under the build plate and peel it off until it is freed from the magnetic bed, after which the ...

At this point, you can basically track any G-Code command and also insert arbitrary new G-codes, for example G1 printing moves (for wipe towers) or M280 commands to control a servo.