We have a bt type tone tester and Genny that only works on dead circuits ( well i have not had the balls to see other wise yet ! ) , a socket and see tone tester and generator that only works on live circuits , and a RDS2000+ cat scan and line generator for under ground services .
The bt one is brilliant for tracing lost cables and plastered over points ! It seems to work best with all other circuits in the property de energised though as they can introduce interference while using it if left live .
The socket and see one is pretty useless to be honest .
And as for the cat scan and line generator , it is the mutts nutzs but at near on ÂŁ2k it wants to be !!!