It's hard to imagine a scenario in which a metal detector on the NYC subway is useful in a way that isn't extremely annoying to the millions of people who carry

It's hard to imagine a scenario in which a metal detector on the NYC subway is useful in a way that isn't extremely annoying to the millions of people who carry their laptops, phones, etc. with them to work each day. (My only experience with a "metal detector" on a metro system is Bangkok's metro. The detector was unplugged at the first station, and everybody was waved past it at the second station.)