After reading this question (https://security.stackexchange.com/questions/65382/is-it-possible-for-a-phone-to-be-transmitting-even-while-turned-off-and-the-batt) on security stack exchange I wanted to know if there exist any methods to degrade the capacity of internal (second) mobile phone batteries as such that they are no longer functioning.

I've already asked this question on security stack exchange and electronics stack exchange but it apparently was not regarded a valid question on both sites.

Because every mobile phone has its unique circuit design, the easiest way to ensure that you cannot be tracked would be to have a mobile phone without internal battery and with the main battery removed or a mobile phone with an internal battery but whose capacity is near zero as such that no circuits can be powered by the internal battery.

1 Answer 1


Any "methods to degrade the capacity of the (hypothetical) internal battery" depend on the implementation of that battery. A battery installed for espionage purposes isn't going to be reachable by regular phone applications, so the only way to drain it is by waiting until that battery is empty at the expected load (plus a safety margin).

If the battery is used to power the regular radio circuitry, any battery that fits in the phone will run out in a day or so. A separate low-power radio could run for a bit longer (a few days maybe), but requires the receiver to be nearby.

Alternatively, insert the phone into a Faraday cage (wrap in tinfoil, build an aluminium/copper/steel box).

It's pretty easy to detect if an espionage circuit of this type has been built into a phone: switch the phone off, and use a radio scanner to find transmissions from the ostensibly-off phone.

  • Please read the question on security stack exchange which I've linked above. I'm not talking about the main battery. Tinfoil does not work for every phone. Regarding your last suggestions please read security.stackexchange.com/questions/59093/…. security.stackexchange.com/questions/12740/… Nov 20, 2018 at 11:24
  • the correct answer on that question was "No, even with any internal capacitors or small secondary batteries, there isn't enough power to get off even a small amount of transmission. Transmission simply requires too much power, even for relatively short range given the type of transmitter in the phone. "
    – Hobbes
    Nov 20, 2018 at 11:31
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    A Faraday cage is basic physics, if it doesn't work you haven't built a good one.
    – Hobbes
    Nov 20, 2018 at 11:32
  • If you factor in improvements in the capacity of internal batteries it will become possible. Can you provide references, that transmission is not possible with the power an internal battery provides? I'm not saying a Faraday cage does not work, obviously it does. However wrapping in tinfoil does not necessarily work. And the Faraday cage bags you can buy wear out pretty easily so they might function for a few days / weeks but fail to do so for longer periods of time. Nov 20, 2018 at 11:45
  • Any secondary internal battery is going to be obvious to anyone opening the device, so no phone you buy in a shop is going to have one. Espionage agencies may modify the occasional phone for spying on a specific target, but unless you're in that trade or a high-ranking government official, getting your phone swapped out for a rigged one is not a credible threat.
    – Hobbes
    Nov 20, 2018 at 12:42

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