The cost benefit analysis is way off here. While an SOS button surely has fantastic benefits, the cost is prohibitive. First, almost all teachers either have a cell phone or nearby landline that functions almost equally in the event of an emergency. Second, these buttons will be used so infrequently, if ever, that their cost does not outweigh their benefits. Third, this buttons will likely cause more problems than they solve: unruly children are bound to misuse the button, and possible over-reactions from police forces which have an ever growing trend toward more industrial, militarized structures are more likely to create a newspaper headline than the reason the button was pushed to begin with. In essence, these buttons are unnecessary and not beneficial enough to spend valuable limited resources on.