Mobile phones send wireless signals to the nearby station in order to help you send your message or connect with another phone.
But the best part about this is that these signals can be captured whether or not you have a mobile phone or not. And the even cooler part about this is that this can be accomplished with nothing more than just a simple headphone jack connected to your laptop/phone.
There is nothing at all you need to do besides sticking a headphone into your jack and placing a mobile phone nearby. Then open Audacity and record it at the maximum sampling rate possible on your soundcard. That’s about it !
Video Demo:
NOTE:
This works remarkably well with older phones (that still use the 2G spectrum), but unfortunately we are still unable to crack into smartphones (that use 3G or 4G spectrum. Argg.. ) using this technique.
But that being said, we are trying our best to crack in. Would highly appreciate any input on this whatsoever. Have a good one!
More interesting stuff:
The hacker Diary 
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Check the phones SAR value. See if there is a relationship between SAR limit and the amplitude of the plot
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