When I worked at a water utility we would occasionally have people breaking into our remote sites like water towers either to vandalise them or climb the assets for the view.

When you just want people off your site ASAP we found providing the operators with remote loudspeakers and allowing them to say "Hey we can see you, we've called the police" was a very effective way to convince anyone that was trespassing to leave.

Though we did lose a few cameras when kids decided to throw rocks at the CCTV system before they left...