Smart fortwo 450 car key replacement button. There is two versions (open/close) in the stl file and they both print out together. Feel free to make your own icons or to add the third button with your own design (there should be both a cabrio and hardtop version of this).

When you slice the file pay attention that the finer details gets included in the top layers of each button. Printing in resolution worse then 0.2mm might not work. I have printed out black versions both in PLA and PETG. Both works good. If you are using heatbed, consider letting it cool of a bit, because the parts might stick really good to the plate. When they are done printing and separated from the bed, just separate them by bending back and forward or just cut them loose.

As for the repair, you open the key on the top where you normally fasten the keychain. Just put a coin in there and twist. It will pop and the black plastic parts of the original key will separate into two parts. Take out the green card in the middle. Consider changing the battery while you are in there. Then just cut away the damaged button with a thin and very sharp knife. Be careful and only cut away the soft part where the button used to be. Use circular motion so the cuts gets nice and clean. Use some sandpaper to remove the last soft parts that you could not remove with the knife. If you printed black buttons the finish doesn't need to be 100%, but other colors might need finer cleanup.

By the way, replacement key is available online, but what is the fun with that.

NOTE THAT THIS BUTTONS PROBABLY ONLY WORK WITH THE FIRST GENERATION SMART FORTWO (about 1998-2007).