The primary purpose of a surveillance system is recording activity and events. Video records of alleged criminal activity can be used as evidence in a court of law to prove or disprove guilt. In a sense a surveillance system is like a witness that is far superior to a human witness because it records exactly what happens and it cannot forget or get confused as a human witness can. A secondary purpose of a surveillance system is to deter criminal activity. For example, criminals that want to rob a particular house and discover that it under surveillance may decide to skip it and pick an easier target. A surveillance system consists of a series of cameras located at strategic points of a home, building or general area that are connected to a central recording unit resembling a typical DVR. The connection to the central recording unit is usually via wires but wireless systems are also available. Generally speaking wire based systems are more reliable than wireless systems but the latter are easier to install.