Recently I have found the Bluetooth feature in the 121GW invaluable, however it's range is a bit lacking and upon inspection it's clear why. The Bluetooth module is behind an EMI shield and behind the batteries. I didn't want to alter the meter by removing/altering the EMI shield, it's clearly required, so instead, I modified the Bluetooth module for an external antenna.
A quick google turned this up, it's pretty simple to do, but you must be ready to work with extremely fine pitch parts (I lost the capacitor and had to steal one from a donor Bluetooth module).
https://www.silabs.com/community/wireless/bluetooth/knowledge-base.entry.html/2015/08/06/_how-to_modify_ble-QAnIOnce done, I grabbed a WiFi antenna (seems to work well enough) and cut it apart and down to fit it inside the chassis without making any alterations. Just used some hot snot to keep it in place.
Did it work? Yeah!
Before I could get a flakey connection from the adjoining room (~5M), now I can connect to it from the other end of the house (~20M away).