c++builder - How to detect the application is about to terminate? -

i'm working on vcl application communicates on bluetooth microcontroller , want execute code right before application terminates.

how can detect application terminate ?

write handler onclose event of main form. reference describes app. shutdown notification as:

when application shuts down, main form receives onclose event, child forms not receive onclose event.

the code executed when form closed means (other process being killed or segfaulting etc.)