An object monitoring system, including a slave system having slave processors (14, 16) and a plurality of cameras (10) for monitoring one or more objects, images of the cameras (10) being processed by respective ones of the slave processor (14, 16), and the slave processors including sensors (30) assigned to respective cameras (10) and at least parts of the fields of view of the cameras (10) to detect predetermined characteristics of the at least parts and generate a trigger in response thereto. A master system has to master processor (20) including agents (34) assigned to at least one of the objects and having one or more of the sensors (30) allocated thereto, the agents (34) each generating an event on receiving triggers from the one or more allocated sensors (30). An event system (6) receives the events and determines whether an alarm condition exists. A user interface system (8) can configure the sensors (30) and agents (34) and respond to events. The monitoring can be used to protect a number of objects, such as paintings and artworks held in a number of locations, from human theft.