The AEC manages the federal election roll. Enrolling is technically compulsory for all citizens but only seems to be enforceable once you are on the roll.
Failure to get your named crossed of a a voting booth (voting isn't compulsory - turning up is) results in a $50 fine.
If you don't vote, you're fined. Presumably the government has a national registry of every citizen. If it's anything like my home country, then you're also obligated to keep the government informed of your current address at all times.