Original Story: http://www.reddit.com/r/RTLSDR/comments/1le3if/so_i_discovered_that_my_hp_laptop_leakstransmits
I was reading through the last batch of documents released by Snowden/Der Speigel, and noticed LOADAUTO (see page 3 of http://cryptome.org/2013/12/nsa-ant-raumuber.pdf)
LOUDAUTOs maximizes the gain of the microphone and then uses the digital signal to pulse-position-modulate (PPM) a square wave signal running at a pre-set frequency. This square wave is used to turn a FET (field effect transistor) on and off. When the unit is illuminated with a CW signal from a nearby radar unit, the illuminating signal is amplitude modulated with the PPM square wave. This signal is re-radiated, where it is picked up by the radar, then processed to recover the room audio. Processing is currently performed by COTS equipment with FM demodulation capability.