I was impressed by this non-intrusion alarm device that is using 4 Bosch Blue Line PIRs. (See our 2017 test: Bosch Blue Line Intrusion Motion Detector Tested)
This is located in a warehouse at a 4-way intersection. If one of the 4 PIRs detects a lift or foot traffic, it sets the red strobe lights off to warn others of oncoming traffic:
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