Summary

I designed this door handle lock (or blocker) so my son (1yr old), who learned how to pull on a handle, wouldn't open the door to the basement. I couldn't find anything that would not prevent me from opening the door if I'm downstairs. Pulling up on the handle is still possible with this.

Note : there are 2 backplates. One has the L coming from the upper part (L-up), the other from the bottom (L-down).

Note 2 : After 1.5 year, it never broke !

Printing:
Backplate : nothing particular. Use 3 perimeters with 0.4mm or 2 with 0.6mm, 15% infill.
Bracket : use 3-4 perimeters, 25% infill, honeycomb or triangle infill (for rigidity).

Assembly : insert the L bracket in the backplate. Install the backplate between your handle and the door (you have to disassemble it)