Travellers at Changi Airport can expect to walk through body scanners more often with 14 machines now installed across the four terminals, as part of moves to boost security amid increasing threat levels.

Body scanners that are able to detect items concealed under clothing within a few seconds also help to reduce screening time, allowing busy airports like Changi to process travellers quickly and efficiently, experts said.

Terminal 4, which has four scanners, was the first to introduce the machines when it opened in October 2017.

Since then, another 10 body scanners have been progressively installed at the other three terminals, Changi Airport Group told The Straits Times.

At T4 - a test bed for the latest technologies - there are also 10 CT X-ray machines. These allow hand luggage to be screened without travellers having to remove laptops from their bags.

With body scanners that are increasingly being used by major airports in the United States and Asia, security personnel - often located in a room away from the screening stations - are alerted when an item is detected on a traveller.

A simple outline of a body is generated to indicate where the object is. The alert is conveyed to officers on the ground who then perform further checks on the particular traveller.

While body scanning technology has been around for more than a decade, earlier models were rejected due to privacy and health concerns. At Changi Airport, the first trials were done as early as in 2008.

To mitigate privacy concerns, body scanners now used at Changi and other airports do not detail the person's actual shape - just an outline.

The machines also use millimetre wave technology to detect both metallic and non-metallic items.

The technology is certified safe and poses no known health and safety risks as it utilises a very low-power non-ionising form of electromagnetic technology, experts say.

The amount of electromagnetic radiation emitted is many times smaller than that emitted by a mobile phone, they add.

While there continues to be resistance from certain groups, primarily in the US, it has not stopped security agencies from pushing the technology through.

Such scanners, they say, are critical to airport security and could have, for example, detected British terrorist Richard Reid.

Better known as the Shoe Bomber, he had attempted to detonate an explosive device packed into his shoes while on an American Airlines flight from Paris to Miami in 2001. Other passengers managed to subdue him.

Apart from the US and Singapore, many other countries, including India and New Zealand, have also announced plans to install body scanners at airports.

Supporting the move, Mr Ong Kok Leong, group general manager of security firm Apro Asian Protection, said body scanners that no longer reveal body contours are in fact less intrusive than pat-downs.

Changi should also get more CT scanners for hand luggage, he said.

"One of the most dreaded experiences in travelling is having to empty laptops and other electronic devices from handheld luggage and repacking them.

"With CT scanners, this will be necessary only on a case-by-case basis if the scanner detects suspicious items in the luggage. The ability to generate 3D images will also significantly reduce the number of false positives," Mr Ong said.

Wider deployment of new technology will not only improve security levels at Changi and other airports, but it will also make the screening process far less stressful for the majority of travellers, he said.