I’ve always planned to monitor my electricity usage. I had previously (about a year ago!) ordered some power transformers from seeedstudio and a six channel ADC for simultaneous three phase current and voltage measurement but never got around to starting the project.
We’ve since had a “smart meter” installed which has a handy LED on it that flashes once every watt hour of energy is consumed. It also has and IrDA port on it but I believe the communications protocol is password protected and will report a tamper state if the password is tried too may times. Because of this, I decided it was best to optically interface with the meter, and best of all, I’ll be measuring the exact amount of power we get billed for. Unfortunately I won’t be able to predict the bill amount (in dollars) as the three phases that come into the house are billed at different rates while this LED pulses the combined usage.