HrRossi

Sometimes there are small boxes on the posts that look like speakers. What are those ? (usually on the top of the posts, with slitted front covers)

I'm from Germany. My guess would be that they are some sort of ultrasound-communication system for situations where it is infeasible to lay wires (e.g. across a busy street), but I never found any specifics about them.
And thanks for the AMA.

Ah, thanks for the clarification. Fröhliche Weihnachten ;O)