New Zealand notes are some of the most hi-tech in the world.
Our so-called paper cash is made out of polymer, a type of plastic, with security features built in to help detect forgeries.
Looking at the 20, on the queen-side it should contain the same bird on both sides.
If you tilt the note, a coloured bar will appear to move up an down the smaller bird, like a hologram.
Each note has an individual serial number, on the bottom left here, and vertically up the right side here.
Polymer notes and the ink used are water-resistant, so there should be no blotches or running ink on the banknote.
If you find yourself with a counterfeit note, put it in an envelope to avoid handling it, and take to police.
And don't forget the feel test, polymer notes have raised printing, which you can actually feel if you run your fingers over it.
Lastly, our notes are tough, hard to rip, while most fakes are made of paper.
(First published April 2019.)