A new Trump-style physical and digital wall is being built by the European Union to deter migrants and refugees as people begin to move again after the COVID lockdowns.

On the border between Greece and Turkey police are using long-range acoustic device or ‘sound cannon’ to deter would-be migrants enter the EU without visas.

The device is the size of a small TV set but can match the volume of a jet engine.

It is just one piece of a new arsenal of physical and experimental deterrents installed during the quiet months of the coronavirus pandemic.

A new steel wall, similar to one constructed on the US-Mexico border, has been built to block commonly-used crossing points along the River Evros.

Observation towers are being fitted with long-range cameras, night vision and multiple sensors. The data will be sent to control centres to flag suspicious movement using artificial intelligence analysis.

The EU has spent $US3.7bn on security technology research following the refugee crisis in 2015-16, when more than one million people – many escaping wars in Syria, Iraq and Afghanistan – fled to Greece and on to other EU countries.

Universities across Europe, working with private firms, have developed futuristic surveillance and verification technology, and tested more than a dozen projects at Greek borders.

AI-powered lie detectors and virtual border-guard interview robots have been piloted, as well as efforts to integrate satellite data with footage from drones on land, air, sea and under water.

Testing has also been conducted in Hungary, Latvia and elsewhere along the eastern EU perimeter.

The aggressive migration strategy has been pushed by European policymakers over the past five years, funding deals with Mediterranean countries to stop migrants and refugees advancing towards Europe.

The policy has transformed the EU border protection agency, Frontex, from a coordination mechanism to a militarised multinational security force.

Meanwhile, Greece is pressing the EU to let Frontex patrol outside its territorial waters to stop migrants and refugees reaching Lesbos and other Greek islands, the most common route in Europe for illegal crossing in recent years.

Armed with the new technological tools, European law enforcement authorities are looking further outside their own borders.

Human rights groups say the emerging technology will make it even harder for refugees fleeing wars and extreme hardship to find safety.

They have taken legal action demanding that details of the AI-powered lie detection programme be made public.

“What we are seeing at the borders, and in treating foreign nationals generally, is that it’s often a testing field for technologies that are later used on Europeans as well. And that’s why everybody should care, in their own self-interest,” said Patrick Breyer of the German Pirate Party.

Migration flows have slowed in many parts of Europe during the pandemic, interrupting an increase recorded over years. In Greece, the number of arrivals dropped from nearly 75,000 in 2019 to 15,700 in 2020, a 78 per cent decrease.

But observers say that there is potential for arrivals to rise again with migrants driven by the COVID-19 pandemic and the sheer number of displaced people which has risen 80 per cent to 272 million, according to the UN.

Amnesty International said the new policy was reward for authoritarian European leaders who have adopted a hard line on immigration.