Final answer:
The subject is about airport security gates that use a thin metal strip to detect metals and indicate their height above the floor, a key component of airport safety measures.
Step-by-step explanation:
The subject of the question refers to a security gate at an airport, which is commonly used to detect metal objects on individuals passing through. This type of gate typically includes a thin metal strip or strips that may be used to sense metallic objects due to their conductive properties. The function of this technology not only identifies the presence of metal but also its approximate height above the floor, which can assist security personnel in pinpointing where on the body the metal is located. These gates use electromagnetic fields to detect metal and are a part of the safety measures implemented at airports worldwide.
The subject of this question is Technology. The thin metal strip described in the question is part of a security gate at an airport. This strip is an essential component of metal detectors used for security purposes, which are a common application of technology today.