Past the initial gate there is no additional security (there are cameras of course, but they are discreet, there is no guards). As you move through the corridors, the spell do not detect presence of any spirits nor artifacts within direct vicinity it does cover backstage, stage and most of the auditorium. As you assensse the ranges, you'd probably would need to visit the offices and restaurant parts to be sure, they resisted the spell.
The rehearsal is in progress with multiple metahumans in the choirs, orchestra, props, dressers. You can single out solists, lead instruments, conductor, lead technicians. The solits are all awakened, most of the others have some kind of chrome. Natural or not to apply for the leading positions or even the best Operahouse in Seattle they need one kind of edge or another. The general emotion background is that of expectation, the day is coming so nervousness is also present and among the hundred or so people the conflicts flare occasionaly over wrong tune, wrong light, wrong turn in the move. again and again some parts are repeated without visible connection between them - the conductor is trying the most difficult part it seems.
As the day is coming to the end, so is the rehearsal soon ending. You stay in backstage corner, hidden from view.