@Michael Cimba
You asked: "Would having the Legacy Base plugged into an outlet with a GFCI on the circuit do anything to the signal?"
No, because only the neutral wire and the phase wire(s) pass thru the detector coil.
@All: A related safety hint (or 3):
The most sensitive of these trips at 5 milliamps (.005 A). It is commonly said that if this amount passes thru one's body, it will knock one off a ladder. More pertinent for the model railroader would be to say that if one is under the layout soldering wires overhead, one will drop the hot iron on one's face. Remember that lying on a concrete basement floor is an effective ground for any type of electric tool with exposed metal parts, if its internal insulation fails. I once had such a drill. Go with a battery drill. There is a reason for the popularity of the 20v battery. 
---Frank M.
