At private premises

The police usually need a search warrant to enter and search private property, unless:

• You agree to the police entering
• The police have a reasonable belief that a serious offence will be or has been committed and entry is necessary to make an arrestTo take into custody. More
• Entry is necessary to stop a breach of the peace
• There has been a breach of an intervention orderCourt order restraining a person from harmful or annoying conduct. More
• The police are chasing someone who has escaped from custodyControl; e.g. when arrested and not free to leave; formerly, care and control of a child. More
• The police have a warrantA document issued by a court directing/ allowing an officer to do something.
  For example: a warrant of apprehension (directing that a person be arrested and brought before a court); a warrant of commitment (directing that a person be arrested and imprisoned); a warrant of distress (directing that a person's goods be seized to satisfy a debt); or a search warrant (directing or allowing a person's house or workplace to be searched). More for arrestTo take into custody. More
• The police have a reasonable belief that illegal drugs are on the premises

See also What if ASIO visit

To get a search warrantA document issued by a court directing/ allowing an officer to do something.
For example: a warrant of apprehension (directing that a person be arrested and brought before a court); a warrant of commitment (directing that a person be arrested and imprisoned); a warrant of distress (directing that a person's goods be seized to satisfy a debt); or a search warrant (directing or allowing a person's house or workplace to be searched). More, police must apply to a magistrate and provide sworn evidenceEvidence given under oath (q.v.). More, either in person or by affidavitA written document sworn on oath before a person with authority to administer it. The person in whose name the document is sworn is called the deponent. More. Once they have a warrantA document issued by a court directing/ allowing an officer to do something.
For example: a warrant of apprehension (directing that a person be arrested and brought before a court); a warrant of commitment (directing that a person be arrested and imprisoned); a warrant of distress (directing that a person's goods be seized to satisfy a debt); or a search warrant (directing or allowing a person's house or workplace to be searched). More, police are only authorised to search a particular premises for specified items. There will also be an expiry date on the warrantA document issued by a court directing/ allowing an officer to do something.
For example: a warrant of apprehension (directing that a person be arrested and brought before a court); a warrant of commitment (directing that a person be arrested and imprisoned); a warrant of distress (directing that a person's goods be seized to satisfy a debt); or a search warrant (directing or allowing a person's house or workplace to be searched). More. The police must serve an adult occupier of the house with a copy of the warrantA document issued by a court directing/ allowing an officer to do something.
For example: a warrant of apprehension (directing that a person be arrested and brought before a court); a warrant of commitment (directing that a person be arrested and imprisoned); a warrant of distress (directing that a person's goods be seized to satisfy a debt); or a search warrant (directing or allowing a person's house or workplace to be searched). More.

Police cannot legally, for example, come to your house with a warrantA document issued by a court directing/ allowing an officer to do something.
For example: a warrant of apprehension (directing that a person be arrested and brought before a court); a warrant of commitment (directing that a person be arrested and imprisoned); a warrant of distress (directing that a person's goods be seized to satisfy a debt); or a search warrant (directing or allowing a person's house or workplace to be searched). More for stolen electrical goods, and then attempt to take your address book. However if they come across evidence of an offence (for instance a marijuana plant) while searching they are entitled to take that and arrest you.