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# Spying on microphones through electrical interference (or something along those lines)
Today I was using my `rtl2832u`-based software defined radio to listen to air
traffic control and such. At some point when I was scanning around in 6m
Ham-Band I noticed two pretty strong signals. I was suprised to even find
anything with an antenna only 50cm of length. However when I
frequency-demodulated any of the two signals I was able to hear myself speak. At
that point I got _slightly_ creeped out and started investigating.
I was able to confirm that the audio was what is being recorded by my laptop's
built-in microphone. My first hypothesis was that this was not actually
broadcast but just interference because the SDR is in the same electrical
circuit as the rest of my laptop.
Later I tried to check if this is a problem in laptops in general by my friend
testing it on their laptop. This did yield an audio signal, however the one of
**my** laptop! (They were positioned about 1m apart.)
When I arrived at home I tried spying on my laptop's mic but wasn't able to
reproduce this behaviour if it was not in the same circuit.
I would really like to know why this is happening. I still can't explain why the
signal is frequency modulated and why it is carried by such a high frequency
(around 50MHz). In case you want to reproduce, here are some details about the
setup:
- Laptop: Acer Nitro AN515-43
- SDR: Nooelec NESDR SMArt v5
- Frequency: 52.125 MHz
In the scenario where this can actually be received from nearby, this is a
somewhat critical security problem since even keystrokes might be recovered from
the audio.
Also if you have any expertise or clues please [contact me](/contact).
**Update:** I have done some research and recognized that this is actually a
very common problem and that it also occcurs on otther machines. People were
even able to decode emission vom VGA and DVI cables to recover the pictures that
is sent. Crazy!
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