Canadian Criminal Procedure and Practice/Search and Seizure/Warrantless Searches/Plain View
A person has no reasonable expectation of privacy in what he knowingly exposes to the public or abandons in a public place.
A peace officer may seize any evidence which he observes by use of one or more of his senses from a lawful vantage point. If an officer is on a premises lawfully and observes items believed to be illegal, it is lawful for him to seize the items. 
For example, police may enter into a house on the basis of preserving property and the public peace, and if on entering they discover stolen property in the household, it may be considered evidence under the plain view doctrine.  Without a lawful search or lawful entrance, there can be no basis for the doctrine.
There are generally three requirements for the plain view doctrine:
- the police officer must lawfully make an initial intrusion or otherwise properly be in a position from which he can view a particular area;
- the officer must discover incriminating evidence inadvertently, which is to say, he may not know in advance the location of certain evidence and intend to seize it, relying on the plain view doctrine only as a pretext;
- it must be immediately apparent to the police that the items they observe may be evidence of a crime, contraband, or otherwise subject to seizure. These requirements having been met, when police officers lawfully engaged in an activity in a particular area perceive a suspicious object, they may seize it immediately:
Lands accessible to the public--i.e. "open fields"--do not have a reasonable expectation of privacy and so are not protected by the Charter where illegal items are found in it. However, the "open fields" doctrine does not encompass all open air private properties.
Observations should be made without violation of the law. Police making observations by trespassing at night is not permitted.
It does not stretch so far as to include a bag found in a locker at a public bus station.
Under s.489(2), where an officer is in the execution of their duties, may without a warrant, seize anything that the officer has reasonable grounds to believe is obtained by, used for, or will afford evidence towards an offence. This power is separate and apart from the common law doctrine of plain view seizure.
See Canadian Criminal Procedure and Practice/Search and Seizure/Seizure of Property for more on seizure.
- R. v. Tessling, 2004 SCC 67,  3 S.C.R. 432 at para. 40
R. v. Boersma, 1994 CanLII 99 (S.C.C.),  2 S.C.R. 488
- R. v. Fitt, 1995 CanLII 4342 (NS C.A.)
R. v. Lauda,  2 S.C.R. 683, 1998 CanLII 804
R. v. Jackson, 2005 ABCA 430
- The Queen v. Shea (1982), 142 D.L.R. (3d) 419 (Ont. S.C.)
R. v. Hébert (1990), 60 C.C.C. (3d) 422 (Que. C.A.)
R. v. Grenier (1991), 65 C.C.C. (3d) 76 (Que. C.A.)
R. v. Dreysko (1990), 110 A.R. 317 (Alta. C.A.)
R. v. Hern (1994), 149 A.R. 75 (Alta. C.A.)
- R. v. Nielsen 1988 CanLII 213, 43 C.C.C. (3d) 548 (Sask. C.A.)
- R. v. Ruiz 1991 CanLII 2410 (NB C.A.), (1991), 10 C.R. (4th) 34 (N.B.C.A.)
R. v. Belliveau and Losier 1986 CanLII 88 (NB C.A.), (1986), 75 N.B.R.(2d) 18
R. v. Jones, 2011 ONCA 632 (CanLII) at para. 54 - describes 4 requirements
- R. v. Boersma, 1994 CanLII 99 (S.C.C.)
R. v. Patriquen 1994 CanLII 3963, (1994), 36 C.R. (4th) 363 (N.S.C.A.); appeal dismissed on other grounds, 1995 CanLII 77,  4 S.C.R. 42
- R. v. Kelly, 1999 CanLII 13120 (NB C.A.)
- R. v. Hok 2005 BCCA 132
- R. v. Buhay, 2003 SCC 30
- R v Makhmudov, 2007 ABCA 248 at para. 19
The use of thermal imaging known as Forward Looking Infared Radar (FLIR) is not a form of search. The heat radiating from the house provides limited information about what is going on inside and virtually no information about the person core biographical information. The emanations exist on the outside of the house and so are exposed to the public.
- see R. v. Tessling, 2004 SCC 67,  3 SCR 432
The use of a sniffer dog amounts to a "search" in law. The use of the sniffer dog is almost exclusively in the realm of drug investigations.
For a sniffer dog search to be valid, the court must ask itself:
- did the officer subjectively believe that there were reasonable grounds to suspect that the accused was in possession of the drugs?
- were there sufficient grounds to reasonably suspect the accused was in possession of drugs?
Reasonable suspicion in this circumstances requires an "expectation" that the accused is "possibly engaged in some criminal activity. As well, the suspicion must be supported by facts that can be subject to review.
As part of the determination of reasonable suspicion it includes the presence of a "masking agent" such as perfumes, colognes or other odour producing products. 
- R v Kang-Brown 2008 SCC 18
- R v Nguyen 2012 ABQB 199 at 97