How does a motion light/sound sensors work?

Select one:

A. By measuring the frequency of the signal that is returned to the sensor.

B. All of these choices ( except none )

C. By reflecting singals off the environment and counting how many there are.

D. By bouncing a signal off of items and measuring the time the signal takes to return to the sensor.

E. By measuring the amplitude of the wavelength that is returned to the sensor.

F. None of these choices.