Maybe it's been posted here and I've missed it, but rather than use some
electronic remote control to turn the DC on and off from around the shop,
what about a system such as is used on buses to let the driver know that
you want to get off -- the "pull cord to signal driver" solution:

Install an outlet and a pull switch (both appropriately sized for the amps)
in an elec box and mount that near/to the ceiling. Take a screw-in eye and
install that near the box so that a string from the pull switch through the
eye will pull the switch the way it is designed to be. Run a string from
the switch and through that eye, and then branch off with string run
through additional eyes around the shop so that a simple pull anywhere
along the runs of string will turn the DC on/off. Now, my shop is only
about 18x13 and I can reach the bottom of the joists above me (about 8'),
so it is easy to run the strings high enough so that I am unlikely to catch
them as I move stuff around the shop. Even for those with higher
ceilings/shorter legs, the system could be adapted by running some eyes and
strings down the walls near each power tool to which the DC is connected.
FWIW, an inexpensive (non-elec) remote control for your DC. -- Igor.

PS: Before I hit send, I DAGS and see that this in mentioned in the FAQ
back in 2000. I did not expect that my idea was original, but with the
regular questions here about DC remotes, what the hey in bringing it up
again. And, kudos to the originals.