Facebook knows everything about you and your personal lifestyle – including what you like to purchase when on a shopping spree. For retailers, such data could be priceless.

Consumer tracking and Minority Report-style facial recognition is also becoming commonplace, often used to judge, typically in real time, the emotions and behavioural tics of passers-by. And based on a patent filing published November, Facebook is developing such a tool.

It aims to improve "service to visiting customers" by "systematically and intelligently" identifying their needs.

The data can then be fed directly to management and staffers to enable better assistance, the filing said.

While it could boost efficiency, some academics have warned it could be seen as an invasion of privacy.

The Facebook patent said the system "intelligently detects and notifies a merchant when a customer is in need of assistance based on the customer's facial expression" and that, in theory, it could "identify a product associated with the customer need."

Based on the filing, the tech-savvy recognition system can be used to send electronic communications directly to the customer's mobile phone. It said that it could be used to host text messages, phone calls and video chats between the customer and a shop's staff.

The facial recognition system, it added, can use a person's expressions to "predict a customer's need" and even determine a subject's "trust level" using data associated with a profile "maintained with a social networking system" – presumably that would be Facebook.

The US tech giant has said it does not comment on patent applications.

The Times reported Friday (1 December) that Facebook is also testing how it could use face scanning to enable payments. It reportedly has more than 300m photographs uploaded every day.

Imperial College London professor, Maja Pantic, told the Evening Standard that the rapid advancement of facial recognition in retail scenarios comes with major privacy concerns.

On the consequences of biometrics, she said: "This is how companies manipulate, sell and collect data about the population. As individuals we must get back the ownership of our own data."

Facebook filed the patent for face-scanning tech for retailers Creative Commons/Pexels