Facial recognition software, scanners that detect weapons and cameras that spot nervous people are some of the technologies that could be used more widely to secure public places, but some would require greater acceptance of surveillance in Europe.
The deadly attacks in Brussels on Tuesday highlighted the vulnerability of Europe's airports and transport systems.
European Union officials, grappling with the conundrum of how to increase security while retaining the openness of society, have convened meetings to discuss aviation and land transport security.