apodicter

An apodicter is a bibelot consisting of a small basin filled elemental acid into which is dipped a rod of calcified elemental thunder. The rod can be raised and lowered, adjusting how much of the acid it is in contact with. This creates a unique arcane resonance which connects it with any other apodicters set to the same resonance. The apodicters transmit all sounds within a short distance (roughly equivalent to the range of normal human hearing) to all other apodicters connected to it. This allows for near-instantaneous communication across large distances.
Though resonances can be set to a very fine degree across roughly 10 million possibilities, anyone who knows or happens to be using the same resonance can hear what is being transmitted. Similarly, if users are in loud areas, it can create a cacophony of sounds around each connected apodicter.
Apodicters function within the air envelope of a realm, but cannot pierce the Sora, making them useless for inter-realm communications.