How do I re-activate (wake?) the monitors from the command line

xset dpms force on

If you have a more complicated system where you need to wake more than one display, you could iterate through them with something like this:

for display in `ps aux | grep -oE "/usr/bin/X\s[^ ]+" | cut -d " " -f 2`; do
    xset -display $display dpms force on;
done