A simple hotkey to move the active window to another monitor.
If we have more than two monitors, You can assign a key to the top, right, etc. and assign the appropriate monitor number.
We make changes to the file ~/.config/openbox/rc.xml by adding the line below.
<keybind key="W-S-Left">
<action name="MoveResizeTo">
<!-- move the window to the second monitor -->
<monitor>2</monitor>
</action>
</keybind>
From what I can gather, Fn key combinations are controlled by the BIOS, and it doesn’t seem to register as a modifier-key at all, so cannot be used generically; unfortunate. Thanks for the xev tip!