Here is a funny anecdote:
   Some time ago I was living in the NRQZ, where the caves are long and
   the EMR spectrum is empty.  I was keeping my private cryptographic
   material on a off-the-shelf android phone with most of the antennas
   removed and their pins grounded, kept in airplane mode since purchase,
   chained to my belt.
   My undiagnosed neurological issues with controlling my hands had
   unfortunately developed already when setting that phone up, and I
   wasn't able to fully manage all the radios and antennas inside the
   device, but I figured it was still pretty helpful.  Like many people
   used to do, I charged it with a 2-wire USB cable to make it hard to
   in/exfiltrate data on it.
   Because this phone was never online, the clock would skew badly.  When
   I needed to use a second factor TOTP, I would have to manually set the
   date on it to get the right code, as it should be with TOTP.  So I got
   pretty familiar with my clock being skewed.
   The people who worked the stores in this area often drove in from the
   edge, since product marketing is pretty heavy there and they wanted
   internet and such.  They would take their phones into the area and use
   the bluetooth functionality with their vehicles or wifi tether them to
   illegal hotspots.
   At some point, my phone started turning it's bluetooth on, on its own.
   I don't know why this happens.  It's happened to me on other devices -
   my present device included.  When I notice, I turn it off.  Phones are
   really used to assuming they're networked.
   Now, when an antenna is grounded, it can still communicate a little bit
   unless the radio itself is disabled.
   So, I was hiking to town for groceries one day because my vehicle had
   broken down, and one of the tellers took pity on me and offered to
   drive me to somebody who could tow my vehicle.  Their car was set up
   for bluetooth with their phone.
   After my trip in their car, my phone's clock was synced.  On its own.
   I didn't know a phone would sync its time over bluetooth.  But now I
   know this can happen.