Large amounts of telecommunications metadata must now be kept for two years by Australian telecommunications companies, under a new law which came into effect on Tuesday.
It covers data on who called or texted whom and for how long, as well as location, volume of data exchanged, device information and email IP data.
It also makes it much easier for authorities to access the records.
The new law has caused heated debate among Australians.
Some have said the laws - an expansion of existing rules on what data can be retained - are justified, but others have raised concerns about civil liberties or potential flaws in the scheme.