a microphone? I know of some places that use them to measure noise pollution (or gunshots in American cities)

gunshot locator?

Sound monitoring station. Wonder what is around that might need monitoring. Industry? Big road? Construction?

Maybe there are some strict rules for the construction project or maybe they just want to keep tabs on things. I have seen those only once or twice, in big cities. They never seem to be permanent, because after a while they disappear again. But I am half a globe away, so...