==> Install security cameras: It is a good idea to install cameras in the hallways and the lobby. It is not easy to identify a real camera and a decoy one. This makes it possible to use a mix of real and dummy cameras and spread them to reduce cost but increase coverage. It acts as a good deterrent for unwanted visitors; however, data from wireless cameras might be intercepted and viewed by an intruder if they are not encrypted.
==> Deploy security personnel: For greater security to important servers and sensitive information in storage places, there should be security personnel on duty to prevent intrusion when the alarms set off.
==> Secure the server ...
Physical security is an important part of the overall security policy of an organization. I have attached a document which discusses the issues.