Thursday, September 01, 2005

Pool IDS

By now you've probably heard the story about the 10-year-old girl in Wales who was saved by the Poseidon computer-aided drowning detection system. According to the vendor:

"[Poseidon] uses advanced computer vision technology to analyze activity in the pool, captured by a network of cameras mounted both above and below the surface of the pool. Poseidon helps lifeguards monitor swimmers' trajectories, and can alert them in seconds to a swimmer in trouble."

While reading comments at Slashdot, several of them reminded me of the value of digital intrusion detection systems. This one by a Poseidon user is very helpful if you want to know more about how Poseidon works.

For example, some critics complain about "false positives," meaning Poseidon sounds the alarm although no one is drowning. Poseidon alarms when a swimmer stops moving below the water for more than a few seconds. If the Poseidon programmers tell the device to alert when people appear to be drowning (i.e., motionless below water for a while), then it is not the device's fault when it alerts lifeguards of this fact.

It should not be Poseidon's fault if someone decides to "play dead" at the bottom of the pool!

If Poseidon alarms when everyone is moving, then that is an example of a real false positive. A false negative means no alarm when someone is drowning and motionless below the water.

Beyond the false positive debate, someone proposed a "drowning prevention system" based on the Poseidon alert. The idea was to raise a portion of the pool (!) under the motionless person, thereby elevating them above the water (!) to safety. This is an example of "prevention" being difficult or too costly. Wherever prevention is impossible, detection should be applied.

Finally, the Poseidon system demonstrates another feature of digital detection: human involvement. Poseidon sounds an alarm, to which human "analysts" (aka lifeguards) must respond. Time is of the essence. Here, "real time" does matter. However, a person could thrash underwater while drowning, and only become motionless after their lungs have filled with water. Still, an alert a few seconds later is better than no alert at all.

On a related note, consider the T.J. Hooper v. Northern Barge Corp. effect. This was the case where Judge Learned Hand (I am not making that up) essentially found tugboat owners negligent for not installing a newfangled "radio" technology (in 1932) that could have warned the boats of an impending storm. Radios were not mandatory at that time on boats, but Judge Hand "legislated from the bench" and essentially made them mandatory because they were so helpful. The previous link uses the same argument to advocate installing DDoS defenses, but one could extend the argument to hold pool owners negligent if they do not deploy Poseidon-like systems.

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