Circle around me!

Hi,
Being interested mainly to know which planes are passing over my head (but in my case they are few with around half hour intervals in between them), I would like to be able to trace a circle around my (or any position why not) and when a plane enters this circle an alarm would ring !
Simpliest way to do it would be to center the wanted position on Windows screen, set zoom and be asked a Km/Miles range.

Would be nice to implement this feature !