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During protests after 2009 Iran presidential election there was a lot of concern that the government will use this sort of technology to find protesters. Some p

During protests after 2009 Iran presidential election there was a lot of concern that the government will use this sort of technology to find protesters. Some people advised that one should remove the battery altogether near protest centers, because putting the cell phone in airplane or even turning it off wouldn't prevent the telecommunication companies from tracking it. The reason they provided was simple: if it doesn't transmit any data while it's turned off, how does it say a different message to the caller when the called number is turned off vs when battery is removed. I mostly forgot about it until I saw this article. Anyone here care to explain if this is true?

conductor 13y ago
When you are turning off the cell phone it sends a signal to the operator (graceful shut down) so the operator knows that you turned off the phone. When you remove the battery the phone has no time to send a message to the operator about the phone going offline so the operator doesn't know for sure whether it's turned off or it is out of the towers range at this moment. Of course this doesn't mean that they can't track turned off phones, it's still technically possible (while the battery is there).
- Crito 13y ago
  It would also presumably mean that the government could compile a list of cellphones that turned off during the protests, while not located at but rather near the protests. To a sane government, this information wouldn't be of much use. To a crazed paranoid government going on purges and witchhunts, this could be all the information they 'need' to find somebody suspect. Of course if you pull the battery, they would also notice the phone dropping off the network (though it would be unclear what the cause was). To a crazed government, the difference might not be too important. If you are ever in the sort of situation where any of this might become a concern, I recommend leaving the phone at home, sitting comfortably on your couch, turned on with the TV on. Of course this precludes using the phone in an emergency, so 'burner' phones with removable batteries may become valued.
pjc50 13y ago
The baseband can lie about the phone being off. So the phone has a blank screen but is still phoning home.
dobbsbob 13y ago
There's also state spyware like FinSpy that makes it seem like your phone is being turned off, or that airplane mode is activated but it's not so they can track you and listen in. Your baseband can also be sent silent sms for precise tracking, or sent commands to auto answer and turn on the mic without you ever knowing. Phones can also be bricked this way if the goal is just shutting down communication. Your carrier can also be coerced into OTA updating the SIM to broadcast your location, intercept voice, or programmed to use rogue BTS set up by police instead of regular towers. Welcome to the dystopian future here's your portable state spying device

conductor 13y ago

When you are turning off the cell phone it sends a signal to the operator (graceful shut down) so the operator knows that you turned off the phone. When you remove the battery the phone has no time to send a message to the operator about the phone going offline so the operator doesn't know for sure whether it's turned off or it is out of the towers range at this moment. Of course this doesn't mean that they can't track turned off phones, it's still technically possible (while the battery is there).

Crito 13y ago
It would also presumably mean that the government could compile a list of cellphones that turned off during the protests, while not located at but rather near the protests. To a sane government, this information wouldn't be of much use. To a crazed paranoid government going on purges and witchhunts, this could be all the information they 'need' to find somebody suspect. Of course if you pull the battery, they would also notice the phone dropping off the network (though it would be unclear what the cause was). To a crazed government, the difference might not be too important. If you are ever in the sort of situation where any of this might become a concern, I recommend leaving the phone at home, sitting comfortably on your couch, turned on with the TV on. Of course this precludes using the phone in an emergency, so 'burner' phones with removable batteries may become valued.

pjc50 13y ago

The baseband can lie about the phone being off. So the phone has a blank screen but is still phoning home.

dobbsbob 13y ago

There's also state spyware like FinSpy that makes it seem like your phone is being turned off, or that airplane mode is activated but it's not so they can track you and listen in. Your baseband can also be sent silent sms for precise tracking, or sent commands to auto answer and turn on the mic without you ever knowing. Phones can also be bricked this way if the goal is just shutting down communication. Your carrier can also be coerced into OTA updating the SIM to broadcast your location, intercept voice, or programmed to use rogue BTS set up by police instead of regular towers. Welcome to the dystopian future here's your portable state spying device