Data transfer without WiFi

[Physikator]

I wanted to measure the pressure in a closed metal lunch box, so WiFi did not work. I managed to create an experiment to generate a sine wave with a frequency corresponding to the air pressure, 1hPa=1Hz. With a second phone I was able do receive the sound and show the frequency=pressure over time. However, this is not very reliable, other sounds disturb the measurement. So I thought of using the vibration alarm as a signal source and a magnetometer as a receiver.
Does anyone know if the vibration generates (enough of) a magnetic field for this to work? And might there be a way to activate the vibration via phyphox?
Thanks a lot!

[Elisabeth Brenner]

Unfortunately there is no option to trigger the vibration via phyphox directly. You would have to connect phyphox to an external sensor that is able to vibrate via BLE. And also I do not think, that the magnetic field outside of the box would be strong enough since it is very quickly declining with distance (proportional to 1/r^3) and also there could be ferromagnetic effects caused by the metal box if it has steel components.
I would rather recommend if you do not need live data to start the measurement before closing the box and read the results after opening it again.