What kind of data are you ultimately interested in, and where do you want to receive it? Microcontroller? PC? Are you interested in just whether there is a current draw or not, or do you want to know what the current draw is? What is the voltage on the circuits? 110VAC? 220VAC?
There are simple doughnuts that go around a lead that have usually a fixed setpoint or maybe an adjustable one, used for indications of under/overcurrent or tripped status. And then there are current transmitters that will generate a signal (0-5Vdc, 4-20mA), or current transformers that will generate a secondary current proportional to the primary current (1000:1, 100:1,...) It is not very practical to make your own current sensors, though, of course, it is possible. A current transducer I have in front of me is from CR Magnetics and it is a 0-30A 4-20mAdc output. Works fine. But you also have to consider how linear your loads are, and whether you want to spring for a True RMS transmitter, which costs more.
More details might get you a more specific answer,
hth,
j.