The arrow shows a small sheet metal screw, M3.5 x 5 mm, glue on a small piece of aluminum foil that is folded over the edge. The aluminum foil on the arm and the screw in the box, form a switch. Other screws M3 x 20mm + nut.

 

The cover for the arm and spring fastened with double-sided adhesive tape. The spring is from a larger ballpoint pen is adjusted so it does not become too heavy.

 

The wheel on the left "Traction-stop-E" attached to an M3 x 30mm screw with nut on the arm