Intrusion detection systems (IDS) are used to determine whether security has been breached and unauthorized access granted to property, resources or data. Examples of perimeter-based intrusion detection systems include buried differential-pressure systems, fence-mounted detection systems, infrared (IR) beam systems, stressed-wire fences, and microwave barriers. Intrusion detection (ID) products that provide perimeter security include both equipment, hardware and software components. They can be used to protect oil fields, prisons, nuclear power plants, chemical processing facilities, embassies, government offices, military bases and archeological sites. There are two broad applications areas: systems for network systems and systems for property and personnel. Intrusion detection systems for computer networks are used to identify security breaches, prevent external attacks, and stop the internal misuse of resources. Pattern-matching detection and statistical anomaly detection are the most common techniques.