The computer that used to fill a room or the stereo system that took up a whole wall now fit in your pocket; technology continues to get small. A dramatic demonstration of how big things used to be are the sound mirrors built in the UK during and after World War 1.
David Barrington writes in Everyone Forever:
Pioneered by the obsessive Dr W.S. Tucker of the Royal Engineers, the concrete sound mirrors were intended to provide early warning of incoming enemy aeroplanes and airships about to attack coastal towns.
But with the development of faster aircraft and the increasing racket from the holiday resort down the road, the effectiveness of the mirrors twindled as an aircraft would be within sight by the time it had been located. The last nail was finally driven into the coffin of this uniquely English folly by the evolution of radar systems, so by 1934 they had tragically became obsolete.
So much concrete, so much effort. What would it take with today's electronics?