In this image you can see a shunt on the Daveyfire.  It's hard to see but it's a loop of wire that goes from the + and  -
of the terminal block on the Gwiz.  This protects the e-match from being fired till it's ready to be fired, it's a dead short.
You can see the loop of the shunt just to the right of my left index finger poking up about 1 o'clock.  It feeds through the
same hole the kevlar bridle loops go through.

The loop of the shunt wire goes forward and the e-match leads run aft through the film cannister.  At this point the GWiz
is plugged in and turned on but the e-match is safed off by virtue of the shunt.  No Switches!