What you need
For visitors
An iPhone with iOS 15 or later, or an Android phone with Chrome 105 or later, and their earphones. That's all: no app and no account.
For the guide
Their phone. On Android they can use the guide app: the microphone keeps working with the screen off or while they use WhatsApp. Without the app, the page locks the screen with a black layer so the microphone keeps picking up sound.
Where there is no signal
Short drops are covered: if the guide's phone loses signal for a few seconds, their voice is stored (up to 30 seconds) and translated as soon as the connection is back. On tour operators' coaches, a 4G travel router with its own wifi. And where there is no network, custom audio guides: the guide prepares them with their own voice and words, visitors download them on joining the room and listen offline.