As I sit here in my office listening to a car alarm go off for well over a minute, I am highly annoyed. But the alarm also caused me to reflect on just how useless car alarms are — perhaps when they were first on the market and only a very small fraction of cars had them, they were effective. But now that they are near ubiquitous and clearly prone to false positives, everyone ignores them, so they no longer are useful; they just disturb the peace.
I think the utility of car alarms are an example of an inverse Metcalfe’s Law, which basically states that the value of a network is proportional to the square of the number of nodes/devices/users in the system. Telephones and fax machines are a good example of this, as is the internet — one fax machine or telephone is useless, but when there are billions of them, things get really interesting.
But car alarms are just the opposite — the more widely deployed they are, the less valuable they become. Does anyone else have examples of things that become less useful the more widespread they are?