Detect when mouse leaves program window

[TerryRitchie]

I could have swore there was a discussion about this before, either on this forum or previous forums, but my searches have come up empty.

How can I detect when the mouse pointer has left the program window?

I seem to remember someone showing how to use an API call ( @SpriggsySpriggs ?) but I didn't have the foresight to add it to my tool box of goodies.

Any suggestions?