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.