[kwhitefoot]

Why not? It's just a simple clip on transformer, similar in design to a clamp on AC ammeter. It is designed for it and legally sold in UK and Norway at least. The current transformer is encased in insulating plastic, it does not make an electrical connection to any wiring only an electromagnetic one. This is what I have http://efergy.com/eu/products/electricity-monitors/elitev1-m... bought from http://www.clasohlson.com/no although Clas Ohlson no longer sell exactly this model.

[efremjw]

Thanks. The efergy clips seem too good to be true! How do I know if they're accurate?

[kwhitefoot]

If you can borrow a clip on ammeter from an electrician you can compare the them. You can also just integrate the readings over a day and then compare that to the electricity meter. The Efergy display units also do this using a running average. This of course assumes that you have a reasonably stable voltage. In most countries this should not be a problem. The Efergy meters measure current and multiply by the voltage you set to get the power, and the sound card solution will need to do the same, while the electricity meter measures power directly.