Actually, maybe the teleporter is in Juni's clothes, and must be above one of the beacons in order to activate the button.
And this is just... I cant exactly quote it, but Zetta said the water doesnt hurt Juni.
And that the thingy teleports her away from it so she doesnt get stranded without it.
How can she get stranded without it if it is attached to her clothing? Or is my definition of 'stranding' incorrect?
The device is sensitive to water, as has been explained, and would be destroyed if it got damp, so it protects itself by triggering if Juni is about to get wet (rain is okay though). She probably just carries it in her pocket or something, it doesn't really matter. It has an 'update' button on its side, which when pressed wirelessly downloads the coordinates from the nearest beacon. It only works at a VERY short range though, due to the bandwidth required to transfer all the data and the risk of data corruption at longer ranges.