A leaked confidential US airport security checklist containing behavioural signs of potential terrorists has attracted criticism.

According to reports, the US government has spent approximately $1billion in a bid to heighten airport security by stationing Behaviour Detection officers across airports.

These officers, known as specialised agents of the Transportation Security Administration (TSA), are given a checklist titled 'Screening of Passengers by Observation Techniques (SPOT)' using which they evaluate passengers.

A copy of the SPOT checklist has now leaked online and some of the signs that indicate that one might be a terrorist include, reported The Intercept: "Exaggerated yawning, excessive throat clearing, widely open staring eyes and face pale from recent shaving of beard."

Since the checklist leaked online, TSA is reportedly downplaying the use of SPOT.

"Behaviour detection, which is just one element of the Transportation Security Administration's (TSA) efforts to mitigate threats against the traveling public, is vital to TSA's layered approach to deter, detect and disrupt individuals who pose a threat to aviation," a TSA spokesperson told The Intercept.

A former Behaviour Detection Officer manager, who requested not to be identified, said checklists such as the SPOT is conveniently used by law enforcement to justify random questioning instead of serving as an actual checklist with specific indicators.

"The SPOT sheet was designed in such a way that virtually every passenger will exhibit multiple 'behaviors' that can be assigned a SPOT sheet value," said the former manager.

"These are just 'catch all' behaviours to justify BDO interaction with a passenger. A license to harass. The program is flawed and unnecessarily delays and harasses travelers. Taxpayer dollars would be better spent funding real police at TSA checkpoints."