What are some ways to prevent unauthorized person from entering building?

To prevent unauthorized access to a building, implement access control systems such as keycard entry, biometric scanners, or keypad locks. Employ security personnel to monitor entrances and conduct regular patrols. Install surveillance cameras to deter intruders and provide a record of any suspicious activity. Additionally, ensure that all Windows and doors are secure and well-maintained, and consider using security alarms to alert authorities in case of a breach.