There has been debate about 'Snicko', the technology used in such situations in Australia, throughout the series after a number of inconclusive incidents.
In the first Test in Perth, England wicketkeeper Smith was given out caught behind on review despite a spike coming after the ball had passed his bat and glove.
That was explained as being because the technology used in Australia has a two-frame gap between the pictures and the sound wave.
Carey is not new to Ashes controversy. He was the wicketkeeper who famously stumped Jonny Bairstow at Lord's in the 2023 series, resulting in a febrile final day.
On his reprieve he added: "Snicko obviously didn't line up. It is just the way cricket goes - sometimes you have a bit of luck.
"Maybe it went my way."
Carey was also asked if he is a 'walker' - the tradition where some batters leave the field without waiting for a decision if they believe they have hit the ball.
He joked "clearly not" in response.
Cricket has always been forward thinking with the use of technology. TV replays were used to adjudicate line decisions more than 30 years ago.
What is now known as DRS was first used in 2008, albeit with some teething problems. In 2009, a report by the BBC said the system was in "crisis".
Gradually, DRS has become part of the fabric and drama of the game, used not only in international cricket but many domestic T20 leagues.
Major controversies are few and far between, however discrepancies can arise from country to country, depending on which technology provider is used.
In this instance, the Snicko system used in Australia differs from the Ultraedge operated in the UK.