Power meters like the Kill-A-Watt are great for keeping track of energy usage, and are also very hackable. The Kill-a-Watt in particular puts out analog signals proportional to current and voltage, ...

Let’s assume, for the moment, that you want a device that measures your running power. Yes, there are reasonable questions and spirited debates that verge on the philosophical about what running power ...

If your goal is to save on electricity, you must first measure the ac current flowing through your appliances. The formula for power is the product of the ac line voltage and the measured current.