P3 P4480 Kill A Watt Electricity Usage Monitor for $22.41. Shipping is free on orders over $25. If needed, use this Filler Tool to pad the order to qualify for free shipping. Here is a screenshot for your reference. Kill-A-Watt identifies power-hungry devices by measuring actual power usage. It features graphic timer of energy consumption by kWh. It usually sells for about $36 or more.