Elements and design: (2) Access control: The next layer is mechanical and includes gates, doors, and locks. Key control of the locks becomes a problem with large user populations and any user turnover. Keys quickly become unmanageable, often forcing the adoption of electronic access control. Electronic access control easily manages large user populations, controlling for user lifecycles times, dates, and individual access points. For example a user's access rights could allow access from 0700h to 1900h Monday through Friday and expires in 90 days. Another form of access control (procedural) includes the use of policies, processes and procedures to manage the ingress into the restricted area. An example of this is the deployment of security personnel conducting checks for authorized entry at predetermined points of entry. This form of access control is usually supplemented by the earlier forms of access control (i. e. mechanical and electronic access control), or simple devices such as physical passes. An additional sub-layer of mechanical/electronic access control protection is reached by integrating a key management system to manage the possession and usage of mechanical keys to locks or property within a building or campus. (3) Detection: The third layer is intrusion detection systems or alarm systems. Alarm systems trigger a response when unauthorized access is detected. They consist of sensors including motion sensors, contact sensors, and glass break detectors. In some jurisdictions, law enforcement will not respond to alarms from intrusion detection systems unless the activation has been verified by an eyewitness or video. Policies like this one have been created to combat the 94-99 percent rate of false alarm activation in the United States