How to detect when laptop power cable has been disconnected?

Question

For the umpteenth time my laptop just shut down in the middle of my game because my power cable had disconnected without me noticing it.

Now I want to write a little

Answer 1

This will probably get closed as not-programming-related, but you may want to check your BIOS setttings.

My Lenovo laptop does exactly what you're suggesting natively. There is a setting in my BIOS for beeping on power status change.