"Teachers, please excuse this interruption. At this time, we ask that you do not allow any students out of your classroom--not to the restroom or the office. We are not on lockdown, but please keep your students in class."
This announcement came about 20 minutes into first period. The students were semi settled, but this riled them up right fast. No one had asked to go anywhere, but then...
"I was just going to ask you for a restroom pass."
"Now, I've really got to go."
Three students. All with "dire emergencies". Another student "helpfully" suggested the corner of the room. And then all of them were at the room's windows, peering out.
(At least they didn't try to leave. One time on an actual lockdown with a room full of freshmen, I had to put myself between them and the door to keep them inside.)
From the windows they saw nothing. I reminded them that they had an assignment, but they weren't interested in that. Then, ten minutes later we got the all clear.
"I don't need to use the restroom anymore. Now that they said we can go, I don't want to."