Or have some fun with https://whitescreen.tv/fake-blue-screen/

I created a little script that ran on startup that would wait a random amount of time between 5 and 15 mins and would just hit the left key once. I dropped it on a dev's computer when he left it unlocked and forgot about it. After weeks of torment, it activated while he had a YouTube video so he figured out it wasn't his fault. He was convinced it was the keyboard and started harassing IT so I had to come clean.

Jokes on me though, every time there was any quirk on his computer, server, or with his code he blamed me and didn't believe me.

It is a good practice to start what we call "Hasslehoffing"

It is where you change the background to a picture of David Hasslehoff every time someone leaves their PC unlocked for a long enough time to change the background. The more it happens, the sexier he gets.

I urge other colleagues to do the same. The only defense there is against that is to lock your PC every time you leave your desk. It really works.