National Security Secrets #3

   National Security Secrets 

#3. An oscillating current can turn any nearby cell phone into a wireless microphone.

This might deserve to be closer to #1,  but how does it work?  Just as importantly, how would one prevent it from happening?

      How to make your phone worthless as a wireless microphone - on the cheap.

Here's a simplified description of the process:

• Under the right conditions, an oscillating current can both provide power for an antenna to transmit and a means to carry the audio that will be transmitted to the antenna.
• It's not the cell phone's microphone that captures any nearby audio - it's the speaker(s).
• When sound occurs nearby it moves the coils in the phone's speakers which can imprint on the current as amplitude modulated sound.
• As the current reaches the phone's antenna it's converted to a signal and transmitted with the encoded sound.
• This can occur with any device that contains a speaker:
• Bluetooth speakers
• Computer or laptop speakers
• Guitar amp

The sound remotely picked up by this technique wouldn't be considered hi-definition.  Depending on how many devices are affected there can be significant amounts of noise, artifacts, and anomalies produced.  But that hardly matters at all.

Because nothing needs to be done to the cell phones themselves (no software or hardware changes) the technique is believed to be immune to any privacy concerns.  The person being listened to knowingly has the device with them, nothing was changed, and nothing new was ever introduced.  It's been so well conceived and designed the main risk is from using it and risking exposure.  Assuming it's only used at early stages of an investigation or fishing expedition then shelved once information is uncovered which can plausibly be claimed was learned by other means... well, you get the picture.

It's really difficult to contest something having been used that isn't known to exist.

That's both clever and sneaky.

 

Originally published on 8-12-2021