By 1 June, the US Transportation Security Administration (TSA) will have removed a total of 250 full-body backscatter scanners from US airports – machines that had been criticized for generating overly detailed passenger images from low-dose x-rays.

The TSA has been replacing those machines with ones that use millimetre-wave technology, which generate images that better protect passenger privacy and rely on radio waves to check for weapons and explosives.

The TSA’s move is yet another example of how governments across the globe struggle to provide effective security while ensuring passenger privacy and efficient queues. As such, airports in the US are trialling new security measures – including facial recognition and iris scanners – to achieve this difficult balance.

Managed inclusion
Currently at checkpoints at Indianapolis and Tampa airports in Indiana and Florida respectively, the TSA is testing a system called “managed inclusion”, in which officials inspect the queues, sometimes with explosive-sniffing dogs, and select passengers to move into expedited security lanes.

The process – also known as behaviour detection – involves each passenger having a conversation with an officer, who asks questions while looking for signs of fear. Passengers who act suspiciously may be subjected to secondary screening measures, such as more invasive pat downs. A similar experiment ran for 60 days at Boston’s Logan Airport in 2011. There’s no word on whether this system will be deployed at other airports nationwide.

As a downside, some critics, such as author and security consultant Bruce Schneier, have said officers practicing behaviour detection are prone to racial and ethnic profiling, or the undue singling out of individuals based on stereotypes. Such profiling has happened frequently at European airports, according to a 2012 study by the consortium Behavioral Modeling of Security in Airports.

Since October 2011, the TSA has been testing PreCheck, a programme in which passengers voluntarily sign up for background checks in return for access to speedier lanes at checkpoints. Expanded last year to 35 major US airports, including most recently San Francisco International and Baltimore Washington, the service is open to elite loyalty programmes members for Delta, United, American, US Airways and Alaska – the only five airlines currently participating. PreCheck is free to frequent flyers, but other travellers may have to pay an application fee to apply via the US Customs and Border Protection's trusted traveller programs, such as Global Entry.

Critics of PreCheck say that technical glitches, such as minor inconsistencies in how passengers' information is presented in various databases, often prevent the effective functioning of the system, resulting in passenger delays. For example, if a paper record has a passenger’s middle initial but the computer has the passenger’s full middle name, the system may fail to make a proper match. The TSA counters that it is working out the kinks in the system.

The checkpoint of the future
In 2011, the International Air Transport Association proposed a collection of airport security improvements that it dubbed “the checkpoint of the future”. Passengers vetted via background checks would have a biometric identifier, such as their fingerprint or iris pattern, in their passport or other travel document. On arrival at an airport, a traveller would be directed to one of three lanes – Known Traveller, Normal or Enhanced Security – according to their biometric identifier. Some travellers would receive intensive levels of checks, such as hands-on pat-downs, while others would speed through.

At a testing centre at Dallas’ Love Field Airport, many of IATA’s ideas are being experimented with in a prototype checkpoint, according to USA Today. One of the highlights is the use of next-generation security cameras, with lenses that are sharp enough to see the faces of passengers from far away in much sharper and more recognisable detail than the present cameras at most US airports and can transmit those high-definition images to hand-held devices carried by guards patrolling the airport. Currently, guards mostly use less sophisticated cameras that only broadcast to monitors in fixed locations. Officials at Love Field hope to deploy the improved checkpoints within the next three years.

Unfortunately, the new systems are expensive. The TSA’s annual budget is $8 billion a year, an amount that some people deem out of proportion to the relative threat terrorism presents.

Sean O’Neill is the travel tech columnist for BBC Travel