This was printed on the Original Prusa i3 mk2

Its a housing and hammer for a standard desk bell. Its anchored to one of the feet of the printer and has a paperclip hinge. When a print is finished, the print bed moves out just enough to trigger the hammer and ring the bell. Works great for hearing when a print is done from another room!

Designed with Onshape.com and is in the public file archive there as well (if editing is needed).