Imagine the security system for the building, which will register the person in front of the doors of the secured object who's interested in breaking into the object.
The security system will send sound beam to the doors: "Leave the secured space and drop what you are doing. If you won't, the security system will call the police immediately". This can be used also to trick the trespasser, when sending the human voice: "We can see you and we are calling the police now" to upset the burglar and to increase the probability that he will leave the object.
We can use directional sound with access terminals like failure detectors etc.
