Paul: The T_sermon goes offline during compile and the window content is greyed and frozen, fine. Could the IDE SerMon button similarly be deactivated during a compile? That would prevent the hole I have stepped into. Or at least have the TeensySerMon ignore (store) the request to open on that port that would go offline at compile start - until compile completes?

Also - would it be legit/easy to use a unique Arduino/Teensy_sermon icon on the taskbar? I have four identical icons for 'IDE' (usually more with other sketches open) and a unique icon would be easier to click after bringing multiple windows to the top between external edit and compile than a random series of Alt+Tab to jump it back to the front.