Galvanic skin response sensors  are used to test the conductivity of the skin. Strong emotions can stimulate the sympathetic nervous system, sweat glands secrete more sweat. This sensor use two simple electrodes attached to the hand, two fingers up enables you to discover a strong emotion, the interesting device can be used to create a project about emotions, such as sleep quality monitoring.

Specifications

Input voltage: 5V/3.3V
Sensitivity can be adjusted by a potentiometer
Easy as reading an Analog pin on the Arduino to see sensor responses

Example Code:

For more details of use and calibration, click on the following link https://wiki.seeedstudio.com/Grove-GSR_Sensor/