Read the power from saver clip
Although you can know the total power you used every month from the bills, you might still interested in the individual power usage of each device. Then, this saver clip must be a good gadget for you.
Safer clip is charged by electromagnetic fields, which is emitted from the wires when you use power. The more power you use, the higher intensity of the field produced. So, what you should do to read the actual instant power of a given device is just clip it on the wired of the given device.