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I apologize in advance if this isn’t the right place to post this, but I though some of you might know the answer to my question.

Many people say that having your phone in your pocket (while not in flight mode) is a bad idea, due to the radio frequency that is being transmitted.

I don’t disagree with RF transmissions being able to cause various types of cancer to various parts of the body, but what I don’t understand, is how one’s phone can transmit RF signals while not in flight mode, but not in ringing/call mode either. What does the phone transmit to the cell tower when it’s not receiving/is in a call?

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$\begingroup$

I apologize in advance if this isn’t the right place to post this, but I though some of you might know the answer to my question.

Welcome. This question is arguably off-topic because it is about the cell network which is not amateur radio, but it can be answered on general principles of radio communications, so I'll do that.

what I don’t understand, is how one’s phone can transmit RF signals while not in flight mode, but not in ringing/call mode either. What does the phone transmit to the cell tower when it’s not receiving/is in a call?

The cell network needs to know where the phone is.

Suppose that there were no such transmissions and you hadn't used your phone for a few days. Then when someone called you, every cell tower in your provider's coverage area would have to transmit that message and listen for your phone's response, because you could be anywhere as far as the network knows. This is a scaling problem: every call started would be occupying some of the network capacity everywhere.

Instead, your phone regularly transmits short messages, and whichever cell towers receive that message well are the ones that will transmit when an incoming call or other data needs to get to your phone. The same thing happens continuously while you are in a call to ensure that audio always gets through even if you move (unless you move to an area not covered by any cell).


Another factor is of course that phones today have many “apps” and other features which are not just making calls but transferring data for other reasons — these are other reasons to transmit that are not making a call. But those are really just the same as calling from a high-level perspective of how the network and protocol works.

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  • $\begingroup$ How often do phones transmit geolocation info to cell towers and how many watts is it outputting when sending such data? Is it the same they output while in a call? I assume not, because then phones would consume too much power when not doing anything. $\endgroup$
    – Coto
    Feb 16, 2018 at 22:26
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    $\begingroup$ @Coto I don't know, and those questions are off-topic as they relate to the specific technology. $\endgroup$
    – Kevin Reid AG6YO
    Feb 16, 2018 at 22:32
  • $\begingroup$ @Coto Well, as to the power consumption, it's because those messages are very short and infrequent, compared to those needed to send audio data. So the average power is low. $\endgroup$
    – Kevin Reid AG6YO
    Feb 16, 2018 at 22:34
  • $\begingroup$ So should such low power and such infrequency actually cause any harm at all? It seems like the idea that you shouldn’t have your phone in your pocket is a myth and doesn’t make much sense... $\endgroup$
    – Coto
    Feb 16, 2018 at 22:37
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    $\begingroup$ Is my low-power VHF transmitter dangerous? Spoiler alert: no. $\endgroup$ Feb 17, 2018 at 2:58

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