At present, the most used is X-ray security checkpoint security equipment. When the passenger's luggage through security inspection door, X-ray scan in turn. X ray is shorter than the wavelengths of an electromagnetic wave, has the stronger than visible light penetration, can even through a certain thickness of the steel plate. Due to the density of luggage items in each are not identical, they absorb x-rays have obvious differences, and therefore shown in the image on the screen as well as depth difference, according to several different shades of the various items shown on the screen, while analyzing the objective comparison, can make the right judgment.
Using two sets of sensor array, can detect the radiation signal of the high energy and low energy, high energy and low energy signal comparison each other, to get the atomic number of inspected items. After X-ray test, the items in the luggage will be shown in the display large shapes, and show the yellow, green, black, etc. (specific to distinguish as shown in the figure below). Safety inspectors can be found out from the screen whether there is any contraband into the luggage. In addition, you can through the electronic instrument, the projection of a certain intensity of X-ray signal into electrical signal, alarm to call the police. Because of the electronic components may produce interference of X-ray, so security is often asked the goods such as laptop computer.
Another frequently used equipment is metal detector door, its working principle is to use the principle of electromagnetic induction. Security on both sides of the rapidly changing magnetic field, the magnetic field on the human body does not produce any effect, but for the metal exceptions, because the metal under the rapidly changing magnetic field will produce eddy current, and eddy current will produce a magnetic field, when my torso to detect the new magnetic field, security will automatically lowing or flashing lights. In addition, similar to the principle of the equipment and hand-held metal detector. When metal detector door alarm, available handheld metal detector to find the location of the metal objects.

The above two are by far the most common way of security, but with the rapid development of science and technology, distances and non-contact, higher sensitivity, more advanced security inspection method is now being developed continuously.