reaches the illuminated spot on the head through an optical fiber equipped with a tiny collimator lens at its end the sound modulated laser light that is reflected from the illuminated spot on the head is then collected by the same lens and made to interfere with the reference lightwave giving rise to interference fringes because the two lightwaves are now at slightly different frequencies the interference fringes move with their velocity proportional to the frequency difference between the lightwaves which is in turn proportional to the velocity of the original signal sound wave a tiny photo detector may be placed so as to cover a single interference spot speckle the detector will show current when the bright interference fringe moves across it with the current amplitude proportional to the audio signal and the current frequency identical to the frequency of the audio signal some electronic signal processing is required to compensate for possible distortions and errors in the system but a need is not foreseen of any major and sophisticated signal processing tasks compressing the detected signal that is pure with little to none of the stochastic information contents of the background noises is optional such a data compression scheme especially when calibrated to the voice of a particular user say the owner of the cell phone leaves a considerable part of the available bandwidth empty and lends it to internet communication or other complementary uses furthermore according to some preferred embodiments of the present invention this facilitates internet services simultaneously with speech transmission and detection finally it is emphasized that the method and device of the present invention use no electronic devices or wires near the head of the user all the detection process is carried.