More than 40,000 fake notes – mostly $50 and $100 in cash – were detected in the past year alone. Authorities warn of a ‘concerning improvement’ in quality.

It’s against the law to knowingly possess or use counterfeit banknotes. So what do you if you’re suspicious?

The Reserve Bank provides advice on how to check your banknotes to make sure they are not counterfeit.

Their recommended quick checks are to feel it, hold it to the light, and then tilt it.

Older 1990s polymer notes show a star and coat of arms through the window.

The newer next generation notes go further: a bird’s wings lift and change colour, a number reverses, and colour rolls across a patch.

If a note feels wrong, the official advice is to bag it, note how you got it, and report and hand it to police.

You can refuse to accept a suspect note (if you feel it is safe to do so).

Your state and territory police are the appropriate law enforcement agencies to contact.

You can also complete an online suspect counterfeit banknote form and submit it to the Australian Federal Police.