I wanna present you the extensions that I needed for so long. It's a GNOME extension that allows you to disable your keyboard with your mouse.

Looking online at options on how to disable a keyboard, all of them involve running several shell commands (getting your device ID, etc) or a shell script. No chance of running those when you have an intruder seconds away. This offers a quick toggle that could save you from that embarrassing "aaaaaaaaaasdffffffff" message.

I hope this helps, and you won't need to get a second keyboard.