The smaller plug in monitors are great for small appliances but which energy monitors should you use to measure electricity usage for larger hard wired items such as Air conditioners, ceiling fans etc. The better option to measure electricity usage for these items would be the energy monitors that are hooked up via the meter box.  The sensor is placed on a cable in the meter box (this should be done by an electrician for any of these type of monitors) then you have a small display screen inside your house, wherever is the most convenient.  These type of monitors measure the electricity consumption for the whole house, so if you were to turn the airconditioner on you would immediately see how much your energy usage has jumped by so you can measure it that way. 

If you have solar panels or any type of photovoltaic system installed on your house you would need to invest in a higher end energy monitor such as the Wattson. With an extra sensor it can detect the flow of power in both direction, whereas with some of the less expensive energy monitors, the information gets confused.

If you have a single phase power with Solar you would need two sensors in total with the Wattson, if you have three phase power with solar you would need 4 sensors in total.