INPEAK power meters work on the basis of a stress sensor that registers the deformation of the crank arm while riding and an IMU that calculates cadence.
These quantities are converted into the power you generate while cycling.
In the TWiN2 double-sided power meter, the power of the right leg and the left leg is measured separately by separate sensors, and then summed and sent to a receiving device (such as a watch) by the left sensor.