Measuring the power consumption of a mains voltage appliance is not a DIY project unless you are familiar with electronics interfacing to mains voltages and know how to do it safely. Any mistake here is potentially lethal for you or somebody else using the device in future.
In practical terms that means buying something to do the sensing for you. Devices to measure power consumption are commercially available and the easiest way to get hold of one would be to buy a consumer gadget that records and displays the power consumption. I suppose it might be possible to have your Arduino interface to a commercial product and collect/display the data centrally, although I'd question whether the value added was worth the effort to do it.