There is a specific model of Casio digital watches that supposedly has desirable qualities for bomb detonation. Anonymous LiveJournal user tongodeon has been following this story for over a year:
A while ago I made a big deal out of the Guantanamo detainees accused of owning Casio F91w wristwatches. In my letter to then-candidate Barack Obama I wrote that “Some have done far worse than wear a cheap digital watch. Some have done little else. In all cases the watches that they were wearing appear to have had nothing to do with anything. The tenuous link between this watch and terrorism is being used as an excuse to detain the innocent alongside the guilty; an excuse for the inexcusable.”
Of the 28 prisoners accused of owning Casio F91w wristwatches, 21 have been released, mostly under the Bush Administration. Prisoner #33, Mohammed Ahmad Said Al Edah, won his habeas petition but it doesn’t say whether he’s actually either been cleared to be released or actually been released. No info on the remaining six.