Special protected areas with extraordinary ecological or scientific value have been set aside and are off bounds to unauthorized visitors.

"To make sure no unauthorized visitors come onto the island."

The purpose of the scope was to reveal unauthorized visitors or spies.

"But I'll alert the guards at the plant to be on the lookout for an unauthorized visitor."

She mentally braced herself to receive another lecture about unauthorized visitors.

Twenty minutes later, he had another unauthorized visitor.

In practice, however, only special permits were required and unauthorized visitors usually turned away.

Smiling, he thought of the surprise unauthorized visitors would receive if they were stupid enough to try to enter this room.

The base is closed to unauthorized visitors, whether by air or from Kamina, a railroad junction town of 100,000.

"Pilot, I have unauthorized visitors," he said calmly into his headset.