VIDEO MOTION DETECTION
There are many methods of detecting intruders into premises. These include such systems as:
- Intruder alarms.
- Fence mounted detectors.
- Buried vibration or electric field devices.
- Active infrared devices.
- Passive infrared devices.
- Microwave devices.
- Video motion detection devices.
These may be within or outside the premises and, besides detecting intruders, can be used as part of a building management system. VMD may often be used either as a stand alone system or integrated with other detection systems. In an ideal world, detection devices would give no false alarms and 100% of genuine alarms. Unfortunately this is not an ideal world, and a certain amount of compromise is necessary. This compromise must be reduced to the most effective and acceptable level to achieve the system objectives.
There are really only two types of alarm, genuine alarms and false alarms. Sometimes mention is made of spurious alarms, unexplained alarms and system failures. These must only be considered as false alarms because the system has alarmed for no apparent reason. A genuine alarm is one created by deliberate nefarious human action, e.g. by movement of a person or vehicle into the detection field or disturbance of the alarm system. A false alarm is one that has no deliberate human input, such as those caused by animals, birds or any malfunction of equipment. One measure of the efficiency of a system is the False Alarm Rate (FAR ) . This is the ratio of false alarms to a time scale, i.e. five per day. The FAR level will depend on many local site considerations. The objective is to reduce this to the minimum without missing any real alarms. Another measure is the probability of detection (PD) rate, which is the ratio of detections to the number of attempts in controlled tests. The ideal for PD is 100%.
