Having to unpack items from your carry-on luggage at the airport, sometimes even removing belts and taking off your shoes, annoys many air travellers. Why laptops must pass separately through the X-ray machine at the security check at most airports is unclear to many people. According to Science Alert, scanner performance is the main factor in this.
Not a problem before 9/11
X-ray machines at airports typically have relatively low power. The rays cannot penetrate certain materials. Parts in laptops thus form a kind of shield under which dangerous objects could hide. Before the terrorist attacks on September 11, 2001, this was not considered a security-critical problem, but afterward.
3D images make unpacking unnecessary
Some airports have more powerful scanners; some even work with computed tomography to create 3D images of the items being checked at security. Removing laptops from bags and backpacks is then actually unnecessary.
Lack of personnel and time savings
Another reason passengers are advised before the X-ray scan to place laptops separately in a basket, empty trouser pockets, etc., is the airport staff shortage. To make the security check process as fluid as possible, baggage must not be sent through the scanner again afterwards.