You wouldn't be doing anyone a favour by committing electoral fraud.
But that aside, although Australia doesn't require any ID on election day, Australians do register with the Australian Electoral Commission (AEC) with their name, address and date of birth. AEC workers have a printed copy of these records on election day. Obvious anomalies like someone with a different age can be reported. Otherwise anomalies like multiple votes from the same address are investigated, I imagine by interviewing the person at that address.
The AEC provides transparency about how it detects fraud and the penalties that can be imposed for people who are caught doing it. The point is that this is quite rare. The AEC's aim is to lower barriers to voting in the first place so that all people can. By detecting anomalies and using tipoffs the AEC estimates the impact of voter fraud and takes a scientific approach to recommend against raising barriers to vote.
But that aside, although Australia doesn't require any ID on election day, Australians do register with the Australian Electoral Commission (AEC) with their name, address and date of birth. AEC workers have a printed copy of these records on election day. Obvious anomalies like someone with a different age can be reported. Otherwise anomalies like multiple votes from the same address are investigated, I imagine by interviewing the person at that address.
The AEC provides transparency about how it detects fraud and the penalties that can be imposed for people who are caught doing it. The point is that this is quite rare. The AEC's aim is to lower barriers to voting in the first place so that all people can. By detecting anomalies and using tipoffs the AEC estimates the impact of voter fraud and takes a scientific approach to recommend against raising barriers to vote.