Physical security comprises the measures — locks, barriers, surveillance, access control and guarding personnel — that protect facilities, hardware and people from physical threats such as unauthorised entry, theft, tampering and environmental hazards. It is a foundational control layer that complements cybersecurity: a system with strong network defences remains vulnerable if an attacker can gain physical access to servers or storage media. Physical security is a standard requirement for data centres and for safeguarding cryptographic key material in cold storage.