Patent ID: 7760090

Claim:
An apparatus for monitoring a portal through an enclosure around a hazard, comprising detector means having a substantially linear field of view and adapted to detect electromagnetic radiation, said detector means being so mounted that said field of view comprises a linear portal threshold that extends along a boundary of the portal so as to detect electromagnetic radiation reflected from an object passing through said linear portal threshold, and distinguishing means to compare signals from said detector means representing a passing object with signals pre-identified as corresponding to the profile of the presence of an object intended to pass through said portal, to distinguish signals from said detector means not corresponding to the profile of the presence of an object intended to pass through said portal and to generate an alerting signal in response, wherein the distinguishing means compares a duration of the detected signal with an expected time for the passage of objects intended to pass through the portal and emits an alerting signal should the detected signal indicate passage of an object traveling faster than those intended to pass through the portal.