Patent ID: 7733226

Claim:
An infrared intrusion detection device, comprising a housing ( 1 ), a window ( 2 ), which is arranged at a front side of the housing ( 1 ) and which is transparent for at least infrared radiation emitted by an intruder, an infrared sensor arranged inside the housing ( 1 ) for detecting the infrared radiation emitted by the intruder, a light guide ( 7 ), which is arranged inside the housing ( 1 ), which has at least one light entrance facet and which has a plurality of light exit facets ( 3 ) arranged at the front side of the housing ( 1 ), a light emitter ( 6 ) inside the housing ( 1 ) for injecting light into the at least one light entrance facet of the light guide ( 7 ), a light detector for detecting light reflected back into the housing by an obstacle in the vicinity of the window ( 2 ), and a signal processing unit for triggering an alarm, when an absolute difference of the intensity of back-reflected light to a predetermined value exceeds a threshold value.