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If you pay attention to NYC infrastructure like I do, you might have noticed little lights that sit on street lamp poles on certain intersections.

For a long time I tried to guess their purpose. I thought that they had somemething to do with street lamps. Maybe indicating when light bulbs need changing. But they do not appear on all street lamps. And sometimes they would be attached to a telephone or a power pole. Sometimes they would be lit up, and sometimes not. They do not appear on all intersections. A mystery, right?

I’ve searched the net finding nothing. Finally I found a reasonable explanation in Time Out New York magazine. The little lights simply appear on the intersections where a fire alarm telegraph box used to be located.

I knew about fire alarm telegraph boxes from an awesome book Underneath New York. You see, those fire and police alarm pull boxes that were retired a few years back in fact were automatic telegraph boxes. They all shared the same circuit which would be normally closed. When somebody pulled the handle, a clockwork mechanism would rotate a little wheel with a pattern of bumps. The bumps would break the circuit and transmit an id of the pull box in Morse code to a nearby fire station. I guess they did not handle collisions — if two boxes were activated at the same type there would be trouble.

I wonder how much electricity is wasted on those things.

Some links:
Interesting, ADT stands for American District Telegraph. I didn’t know.
Some pretty cool pictures of fire telegraph control rooms.
A site about Fire Alarm Telegraph Systems