The rules for Duty Free carried as Hand Luggage is that the bag must remain sealed and unopened and bought from an accepted location. Further, you must be on a direct flight from the airport of purchase / pickup or stow it in your checked-in baggage.Your total allowance is 2.25L per person in your group over 18 (can be pooled)
As per the Travel SECURE website:
You can purchase duty free items:
- at the last airport you stop at before entering Australia if the duty free retailer provides a gate delivery service
- onboard the last leg of your flight to Australia
- upon arrival at an Australian international airport.
If you are flying directly into Australia from an international airport and Australia is your final destination, any duty free liquid, aerosol and gel items you purchase and pack in your carry-on baggage [emphasis mine] are subject to the Australian Government's Immigration and Border Protection quantity restrictions (mentioned below).
If you are aged 18 years or over, you can bring 2.25 litres of alcoholic beverages duty-free into Australia with you. All alcoholic beverages in accompanied baggage are included in this category, regardless of where or how they were purchased.
Aviation security regulations may restrict the volume of liquids that you can bring into Australia as hand luggage. As an alternative, duty-free alcoholic beverages can be purchased in an airport duty-free shop on arrival in Australia. For more information about the restrictions, visit the TravelSECURE website.
Families travelling together can pool their duty-free concessions.
If you happen to be transiting countries on your way to Australia, your carry-on Duty Free luggage WILL BE FORFEIT before boarding your Australian leg of your flight. This is due to in-flight liquid, gel and aerosol restrictions (100ml of liquid only).
If you are transiting through an international airport of another country after departing Australia, you will be subject to liquid, aerosol and gel restrictions at that airport. Restrictions in that country will determine if the items are allowed.
- Liquid, aerosol or gel items must be in containers of 100 millilitres (volume), 100 grams (weight) or less.
- Containers must fit into one transparent and re-sealable plastic bag like a snap-lock sandwich bag.
- The four sides of the bag's sealed area must add up to no more than 80 centimetres (e.g. 20x20 cm or 15x25 cm).
- Only one bag is allowed per passenger, with exceptions for carers who may carry the bag/s for people in their care, including children.
[!] Containers larger than 100 millilitres or 100 grams, even if only partially-filled, will not be allowed through the security screening point. For example, a 200 gram toothpaste tube that is half-full will not be permitted.
At the screening point all liquids, aerosols and gels in your carry-on baggage must be separately presented for screening.