Section 8 of the Canadian Charter of Rights and Freedoms protects your right to be free from an unreasonable search or seizure. With limited exceptions, the police must obtain a judicially authorized warrant and present you with a copy of that warrant to search your home.
To obtain a warrant, the police must have reasonable grounds to believe that evidence of a criminal offence will be found in the place to be searched. The warrant will set out the specific parameters for the search.
If the police are lawfully in a place, they can seize evidence of a criminal offence that is found in plain view without a warrant. For example, the police may be able to seize drugs or indicia of drug trafficking found in plain view while they are in your home responding to a 911 call.
If the police arrest you for a criminal offence, they can search you and the area immediately surrounding you for weapons or for additional evidence of that criminal offence.