There's 'arrested' and 'detained'. In the US police can detain anyone for up to 48 hours (72 hours if it's a weekend or long holiday). If they don't file charges by then they have to release you.
For a silent/duress alarm it's easy to cross reference the person at the door with a list of personnel authorized to be in the facility. Security in a scenario like that would normally ask for an ID, radio it back to their security office to validate the person is on the access list for that office/building/facility/etc and then do a quick walk-around.
For a silent/duress alarm it's easy to cross reference the person at the door with a list of personnel authorized to be in the facility. Security in a scenario like that would normally ask for an ID, radio it back to their security office to validate the person is on the access list for that office/building/facility/etc and then do a quick walk-around.