Abstract: A system for monitoring the presence of persons within a zone, the system comprising: one or more remotely detectable markers, each capable of being carried by a person; a first sensor arrangement capable of identifying the presence of the body of at least one person within the zone; a second sensor arrangement capable of identifying the presence of at least one marker within the zone; and a processing arrangement responsive to the first sensor arrangement and the second sensor arrangement to generate an alarm signal if the first sensor arrangement identifies the presence of a body without the second sensor arrangement identifying a marker corresponding in a first predetermined manner to that body.

Abstract: A technique is provided for providing total flexibility of control of any desired operation within an environment where personnel work, such as an office suite. The location of transponders is determined by a location system. A user arbitrarily selects a convenient region for controlling an operation and the location system registers this in a memory. The location system then determines the position of each transducer and, when a transducer is within one of the selected regions, the location system responds by controlling the operation. For example, a region may be selected entirely arbitrarily so as to control room lighting.

Abstract: A location system comprises a plurality of transponders whose locations are detectable by a base system. The base system interrogates (51-55) the transponders one at a time in accordance with a schedule of consecutive time slots. In response to a priority request received (53) from one of the transponders, the base system interrupts the schedule and interrogates substantially immediately (56,57,55) the signalling transponder so as to determine its location with minimal latency.