gatekeeper

Example:The guard stationed at the gate was alert and prevented anyone from entering without authorization.

Definition:A person whose job is to stay awake and watch for danger, trouble, or unwanted people in an area.

Example:The doorkeeper at the museum was very strict and only allowed pre-registered visitors to enter.

Definition:A person whose job is to guard, control, or admit people at a door or entrance.

Example:The software filter acts as a gatekeeper, blocking known malicious traffic and safeguarding the company's network.

Definition:An electronic circuit or device that allows some signals or frequencies to pass through and blocks others.