Put your project in stealth mode with these silent Soft Tactile Switch Buttons.
Tactile switches are standard input "buttons" on electronic projects. These work best in a PCB but can be used on a solderless breadboard as shown in this tutorial. The pins are normally open (disconnected) and when the button is pressed they are momentarily closed.
They come in a pack of 10, they're pretty handy so you'll want to keep them around. These are great for projects like the PiGrrl, PiGrrl 2, Pocket PiGrrl or PiGrrl Zero since the elastomer buttons feel better than the default clicky ones. The activation force isn't linear or documented, but a similar switch is listed as 120gf.