Not to be pedantic but I think the headline is fine.
If you simulated a fire in a building for training purposes and upon activating the fire alarm, it got broadcast to emergency services when it shouldn’t, you did accidentally broadcast the fire alarm, simulated or not.
The “accidentally” already implies it was done in error, suggesting it was not an emergency. On the other hand, if it was a real emergency, and just wasn’t meant to be publicly broadcasted, I feel like the headline would’ve looked different.