Building management systems are commonly installed in large scale projects which have extensive electrical, HVAC, and mechanical systems. Close to 40% of a building's energy usage is from systems that are linked to a building management system. In addition to internal systems, building management systems are also linked with access control such as access doors controlling and turnstiles that allow access and outlet to the building, and other security systems such as motion detectors and CCTV. Elevators and fire alarm systems are often linked with a building management system for monitoring purposes.