I think they are devices meant to block cell phone signals in case of a terror attack.
Interesting. I was thinking it would be easier to have the cell-phone providers on speed dial, but what if the private firms balk at shutting that whole sector down?
And then it would also interfere with emergency response.
But having little black boxes near critical places (airports, train stations, stadiums, etc.) they could maybe jam the signals going to a remote detonation bomb without shutting everything down. Of course then you need to hope they cover most things.