This is a force sensitive resistor with a square sensing area of 40x40mm. The resistance of this FSR varies according to how much pressure is applied to the sensing surface.
The lesser the resistance, the stronger the force. The FSR's resistance will be more than 1M when no pressure is applied. This FSR can detect applied force ranging from 100g to 10kg.
Two pins extend from the bottom of the sensor with a 2.54mm pitch making it breadboard friendly. There is a peel-and-stick rubber backing on the other side of the sensing area to mount the FSR.

To determine the force applied, just connect a resistor to make a voltage divider and measure the voltage at the junction. These sensors are easy to set up and work well for monitoring pressure, although they aren't particularly precise. You can use them to feel if it's being squeezed, but you shouldn't use them as a scale.

SPECIFICATION