You can never tell when your key will break inside your door knob and when it happens, most often than not, we tend to to more damage to it and the door itself than fix the problem.
However, the video shows how you can safely remove your broken key with a heated plastic straw.
See video here 👇
https://twitter.com/SanjuSh51614314/status/1286292776368238594?s=19
Video source : Twitter
