TSA officers pat down shoulders during security screenings primarily because the Advanced Imaging Technology (AIT)—the full-body scanner—frequently triggers "false alarms" in that area. Shoulders are prone to alarms due to bunched-up clothing, thick seams, shoulder pads, or even heavy perspiration that the scanner interprets as a foreign object concealed under the fabric. Additionally, the AIT requires passengers to stand with their arms raised; if a passenger has limited mobility and cannot fully clear the "sensor field" above their head, a targeted pat-down of the shoulders and upper arms is mandatory to resolve the anomaly. The pat-down is a "resolution" technique designed to ensure that no metallic or non-metallic threats (like plastic explosives or ceramic blades) are hidden in the hollows of the collarbone or under the armpits, areas where the scanner's millimeter-wave technology can sometimes experience "shadowing."