Since the buttons of the car keys have broken and the ones I did as substitution were not comfortable I decided to try to make new ones better and more functional.
Step 1: Materials and tools
To realize them you don't need much, just get or buy the oyumaru (it's the ideal material to create molds of things and objects you want to replicate) and Fimo (this is also a material that I didn't know and, as the oyumaru, I discovered thanks to other instructable authors who have reported them to me and recommended). As materials, you don't need any more. Just only a small pan, the oven and eventually a cutter.
Step 2: Molds
First you have to create the molds. If your buttons are not broken you can use them to create the molds. Mine was not usable so, to make the molds, I recreated copies of the buttons using pieces of shoe sole ( the same i used to make the bike mud flap). Make the molds it's really quite simple: put water into a saucepan and bring to 80°c (176°f). Reached the temperature soak up the oyumaru (for the two molds I used half bar) and leave it for three minutes. Past three minutes pull it out (at this point you will see that the oyumaru has become softer and more malleable) and push on the button so as to create the mold. Let cool and remove the button. The mold is done! For the other button repeat the same operations.
Step 3: Create the buttons
It's now time to create the buttons! Take a piece of fimo and work it with your hands. When it seems quite soft press it into your mold. Let cool the fimo, in this way it will harden a bit and will be easier to remove it from the mold.
Having seen that it was soft and pulling out the printed piece has deformed, I put the mold into the freezer for a bit of time so to harden more. Once extracted, you can cook it.