A 3D printed battery powered bluetooth speaker made with the speakers from a 2007 MacBook Pro. Sources and build instructions on thingiverse: https://www.thingiverse.com/thing:2458126
The onboard Bluetooth device of the Raspberry Pi Zero W and the Pi 3 can be disabled by adding “dtoverlay=pi3-disable-bt” to the /boot/config.txt file. Wifi can be disabled with “dtoverlay=pi3-disable-wifi”.
More boot config options for the Raspberry devices are documented here: https://www.raspberrypi.org/documentation/configuration/config-txt/
The German company Sensorberg offers Bluetooth Low Energy (BLE) beacons called “iBeacons” and a SDK for proximity detection.