strange device

here is a mysterious thing i saw on the way back home tonight. it’s a massive black box on the left connected with some wires to some electronical thing on the right. it’s location was outside a strategic British Telecom telephone exchange (i shall not reveal it’s actual location, nor indeed how i know this information)
so what is the device ? is it likely to go boom ? is it part of a telephone exchange ? is it a congestion charge enforcing device ?
who knows. who cares