As a member of Ad-staff last year on camp we had had a policy in place on how to handle emergency situations. The Ad-staff team were known as Crisis team A and the area directors were known as Crisis team B and each team had specific duties to do if one of the alarms were sounded.
At the weekly UL meeting we stated that there would be an LBD (lost bather drill) at some point that week. Only the Waterfront director and CD knew when it would actually happen.
On the first night of each session, the unit staff explained to campers about the alarms and what they should do if they hear one. They explained that it was very similar to having fire drills at school where we need to practice what do in case of an emergency.
That way when the alarms sounded both the campers and staff remained calm and followed proceedure.

Being international, i'm not sure of the legalities that you are refering to but one of the standards for ACA accreditation is that the is a policy in place and that all staff and campers are aware of it and know what to do whether it is a drill or the real thing. It also states that drills should be carried out to ensure that good practice is being carried out.

In four summers of camp, I have never known any campers to get upset and we did have to have a real alarm as a girl had gone missing (she wandered off because she wanted to go for a walk on her own but didn't tell anyone!!). The staff realised that the alarm was real but still responded in a mature and responsible way not alerting to their campers that the drill was real.

I personally feel that staff should be warned that there will be drills throughout the summer but not specifically when.
Campers presume every alarm is a drill and just like at school respond accordingly.
The main point is how we as staff members respond! If we act cool, calm and collected there is no reason why your campers should panic.