I photographed these various Intrusion Detectors at Eglin AFB and the NMoUSAF. During Operation Igloo White, these were dropped into areas of Vietnam that US Forces were not allowed so that enemy troop movements along the Ho Chi Min Trail could be monitored.
Seismic Intrusion Detectors
Left to right: ADSID (Air Delivered Seismic Intrusion Detector); COMMIKE(Commandable Microphone); and ACOUSID (Acoustic and Seismic Intrusion Detector)