AC Current Sensor
Non-invasive AC Current Sensor Transformer. It is a current transformer that can be used to measure AC current. This non-invasive current sensor clamped around the supply line can measure a load and allow you to calculate how much current pass through it. It can help build an energy monitor or an over-current protection device for an AC load.
Clip it around the current source that you wish to measure, and it will produce a (very) small AC voltage proportional to the current. The cable is terminated on one end with a standard 3.5mm jack (like a headphone jack).