"Perhaps when they were first on the market'¦[car alarms] were effective. But now that they are near ubiquitous and clearly prone to false positives, everyone ignores them'¦[It's the inverse of] 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.'¦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?" McIntyre's readers suggested banner ads, nuclear weapons, and, ahem, venture capital.