Use <Unmap> and <Map>:
bind . <Unmap> {puts "Someone just iconified me."}More sophisticated programming recognizes "that toplevel bindings apply to every child widget, so you should also test that the widget is a toplevel" and also that "Unmap will also happen when you switch desktops, so you have to ... test the state" (in the words of Donald Arsenau ...):
bind . <Unmap> {unmapper %W}
proc unmapper W {
if {[string equal [winfo toplevel $W] $W] &&
[string equal [wm state $W] iconic]} {
puts "Minimizing $W."
}Bruce Hartweg adds ..., "Also note that with some WMs the multidesktop is handled the same as an iconify, so you still might get 'false' hits."