The SparkFun Current Sensor Breakout is a High Precision Card that uses the ACS723 for Moderate AC and DC Current Detection Applications. The ACS723 Sensor uses a Hall Effect Sensor to Emit a Voltage relative to the Current that flows through the IP + and IP- Pins on the Board. The advantage of using a Hall Effect Sensor, specifically, is that the Circuit Being Detected and the Sensor Reading Circuit are Electrically Isolated, which means that although your Arduino is Operating at 5V, the Detected Circuit may be Operating at Higher DC or AC voltages.

SparkFun RGB and Gesture Sensor - APDS-9960