Electrical Testing using compass?

I know the 3GS can be used to detect metal using the compass, however today I was fitting a new light and used a pen device that when you put it near a live wire it glows red to tell you there is a current there, however I was wondering if the iphone can do this by using the internal compass?

Is there an effect on the compass when electricity is pass near to it?

Are there any apps already out there that can do this?

Thanks