I appreciate it :D

Those two questions are spot on.

Voice cannot be transferred yet. Re-broadcasting might require a bluetooth meshnet.

Vibrations are a great idea. They are not that battery intensive. They also can be detected by 3rd party tech.

Both were added to the list of ideas. Thank you!!

I haven't done any effort there, because I want to get this into hands.

Have you considered alternating signals using different radio frequencies? And then use differences in signal arrival times for more accurate location? Also I guess using different bands might be more universal, as signal loss would be different depending on environment and band used.