The new 12-sided £1 coin - which comes into circulation on Tuesday - has a hidden security feature to make it difficult to counterfeit.
It is thought to involve material inside the coin itself which can be detected when electronically scanned by coin-counting or payment machines.
But officials at the Royal Mint have not released any further details.
Other security measures include an image that works like a hologram, and micro-sized lettering inside both rims.
As a result, the Mint claims it will be the "most secure coin in the world".
It will replace the existing £1 coin, of which about one in 40 are thought to be fake.
"It's been designed to be fit for the future, using security features that aim to safeguard our currency, and currencies around the world, for years to come," said Adam Lawrence, chief executive of the Royal Mint.
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