I have been using the Amprobe / Pasar Current Tracer package for about 6 Years, and it's by far the best, most reliable and most flexible I have seen.
Can't quite remember the complete kit's model number, but I'll list the individual items for reference [the original kit came in an irritatingly small plastic box which has become filler for the Recycle Bin!]:
Receiver ["Probe"]= Model number P26,
Transmitter = Model number T300 (6-300 Volts AC or DC),
for Voltages of 300-600 VAC / VDC, the T300 Transmitter can be run through the "Wide Range Converter" Model number 600CKA.
This tracer can be used on live circuits, or on dead circuits / conductors (via a 9 volt drycell).
The Transmitter pulses a cadence of 6 KHz tones, which hasn't yet interferred with any sensitive equipment.
After using it for about 3 months and across various types of projects, I had the feel for any "wierd" readings that would pop up.
Seems like we paid over $600.00 for it back in 1996, but it was well worth every penny!