P3 Kill-A-Watt P4460 Electricity Usage Monitor for $32.14 shipped. Kill-A-Watt is a tool that helps identify power-hungry devices by measuring their actual usage. This is a newer version that includes cost calculation in addition to power usage and other related measurements. We have a couple of them and have found them to be, uh, fun, amusing, and more importantly, very useful. Here is a review for your reference. Most places have it for about $40.