...is the monitoring of the behavior, activities, or other changing information in your operating environment. This monitoring can be passive or active, overt or covert. It can be performed by a security professional who is trained to observe and report, a licensed investigations professional, or through a variety of optical and electronic devices.

Surveillance can happen in real-time, near-real time, or the video collected can be stored for future reference. The difference between the three are quite important from a security perspective. Real-time allows for immediate intervention if required, while near-real is usually a way of saying that nobody's watching, but an alarm will tell me when to look. The storing of video is usually only used for forensic purposes - who did what when. It has a limited deterrence capability.

Surveillance can be done physically, on-site or remotely. In the latter two situations surveillance devices can be used to perform patrolling functions.

All surveillance activities are performed within very strict legal and ethical guidelines.