We recommend :

Chose detector which is able to display banknote or its part in infra-red spectrum. Euro counterfiet with infra-red protection imitated was still not captured up to the moment.
Banknote detail magnified minimally 10x with side incident light for inspection of intaglio presence.

Illustrative example of displaying the IR protection of genuine 20 EUR banknote and of counterfeit:

By detector with display ability you easily recognize counterfeits from genuine banknotes without the problem.