When traveling on airplanes you must check in at airports and your luggage and carry-on bags have to go through an elaborate screening process. The machines that perform this duty are typically metal detectors or X-ray scanners.
The principle of a metal detector is made up of wire coils, a transmitter and current creates an electromagnetic field. The direction of the current flow is reversed several thousand times every second. After a few seconds, this current or pluse slows down and disperses. Any metallic object that enters this electromagnetic field will influence the speed of the current and set off on alarm.
X-ray is unlike visible light, humans cannot see X-ray. X-ray is used in various scenes for example hospitals, an airport and so on. In an airport, X-ray technology is used in CT scanners. CT scanners are more complex than metal detectors and can analyze chemical components in addition to metallic objects. The objects which are known to be dangerous are removed from the suitcase.
Tn busy airport, large trucks which pull up beside containers that hold the suitcases, bag and other cargo with built in X-ray scanners are used to scan large amount of baggage at one time.