HHelen
I mean, the emergency key could be tamper-sealed, but in this case you might as well have a non-locking fastener and a tamper seal on the belt itself. Basically, if the wearer comes home with a broken seal, they better have a good explanation why the belt had to come off.
Lock+key still has the advantage of potentially warding off drunk tomfoolery or pushy dates a bit more effectively than a belt with just a seal.