The pool has cameras under the water and over it, and software that watches every swimmer and alarms if one stops moving on the bottom, because a lifeguard cannot watch forty people at once. At about half past one the system alarms on the deep end, marks a body on the bottom at the six foot mark, and the pool is empty, the cover is on, and the lifeguard station's screen shows a swimmer that the underwater camera cannot.
I am the pool's duty manager, and the detection system's alarms come to my radio.
How the system works.
Cameras in the pool walls look along the water and cameras in the ceiling look down, and the software finds each swimmer as a shape and follows them. A shape that sinks and stays on the bottom for more than a few seconds triggers the alarm: a tone at the lifeguard station, a mark on the screen showing where, and a log entry.
At night the pool is covered, the hall is locked, and the system is left running because the cover does not stop the cameras and the insurer likes the log.
At about half past one, most nights, the system alarms on the deep end.
The screen marks a body on the bottom at the six foot mark, near the wall, still. The log records a drowning alarm, and the software's confidence figure, which is high.
The pool is covered. The hall is dark. There is nobody in the building.
The overhead camera shows the cover, flat, and the software's mark drawn on it where the body would be underneath.
The underwater camera at the deep end, which looks along the bottom at the six foot mark, shows the bottom, tiled, lit by the underwater lights, empty, and the software's mark drawn on that too, around nothing.
The software sees a shape. The camera that it sees it through shows tiles.
What has been checked.
The software, updated, and the cameras, cleaned and replaced. The company's engineer watched the alarm on our system and pulled the frame the software alarmed on and ran it through their own analysis and said the software had found a human shape with the confidence it would find a real one, in an image with nothing in it, and that he had never seen that and would take it back to his people.
The water. Drained in the spring for the annual work, and the alarm came every night on a dry pool, on the bottom at the six foot mark.
The lifeguard station. The alarm tone sounds there at half past one, in an empty hall, and the night security guard, who does the round at two, has heard it and has come to me about it, and has since asked to do the round at one.
The position.
Six foot mark, deep end, near the wall, on the side by the steps. That is where a swimmer who has gone down off the steps ends up.
The pool was built in 1971, and in its first summer a boy went down off those steps and was not seen for the ninety seconds that matter, and the plaque in the foyer that nobody reads has his name and the date, and the building has had a drowning detection system since it became possible to have one, because the manager who ordered it had been a junior lifeguard here in 1971.
What is done about it.
The night alarm is on the log every night and it is annotated, and the insurer's inspector has seen the annotation and said the system was clearly sensitive, which is the word he used, and that he would rather it were.
The system is not switched off at night. The manager who ordered it is retired and I asked him, once, and he said please do not, and I have not.
What I do.
I manage the pool.
The one thing I have changed is that I do the last check of the night before the cover goes on, from the deep end steps, and I look at the bottom at the six foot mark before I put the lights out.
The reason is a night in the winter when I was late and the cover was on and I was at the lifeguard station when the alarm came, and I looked at the screen, and the underwater camera, which shows tiles, showed the tiles and, for the length of the alarm, the cover above them from below, lit by the underwater lights, and pressed up against the underside of the cover, from the water side, flat, the way a hand presses on glass, a hand, small, and it moved along the cover towards the steps, and the software followed it, and the alarm ended when it reached the wall.