Canadian Criminal Procedure and Practice/Arrest and Detention/Investigative Detention
The police have a common law right to detain people for investigative purposes. The investigation must be based on a "reasonable suspicion that the particular individual is implicated in the criminal activity under investigation" for it to be considered lawful.
An officer's grounds to believe an offence has been committed will fall short of being "objectively reasonable and probable" allowing for an arrest. It the officer instead has a "reasonable suspicion" that the suspect was involved in a criminal offence, it may be enough to justify investigative detention.
Right Against Arbitrary Detention
Section 9 of the Canadian Charter of Rights and Freedoms provides that
9. Everyone has the right not to be arbitrarily detained or imprisoned.
The "purpose of s. 9, broadly put, is to protect individual liberty from unjustified state interference" Thus "a detention in the absence of at least reasonable suspicion is unlawful and therefore arbitrary within s. 9"
The burden is upon the applicant to prove that the accused was "detained" within the meaning of s. 9 which must be proven on a balance of probabilities.
Types of Detention
A person can be detained physically or psychologically.
Psychological detention has three elements:
- a police direction or demand;
- the individual’s voluntary compliance with the direction or demand resulting in a deprivation of liberty or other serious legal consequences; and
- the individual’s reasonable belief that there is no choice but to comply
Detention by police does not continue subsequent to release on terms of bail, and so entitlements such as the right to silence do not apply.
The purpose for detention can have concurrent reasons, such as conducting traffic enquiries while making observations of drug related offences.
An officer cannot detain a suspect on the basis of a hunch.
- R. v. Grant 2006 CanLII 18347, (2006), 209 C.C.C. (3d) 250 at para. 8 and 28 (ONCA)
R. v. Nesbeth, 2008 ONCA 579 at para. 15-17
R. v. Harris, 2007 ONCA 574 at para. 17
R. v. Suberu 2009 SCC 33 (CanLII), (2009), 245 C.C.C. (3d) 112 at paras. 23-35
- R. v. Earhart, 2011 BCCA 490 
- R v Harding 2010 ABCA 180 at para. 18
R v Yague, 2005 ABCA 140, 371 AR 286 at paras 7 - 9
R v Nolet, 2010 SCC 24
- R v Mann, 2004 SCC 52 at paras 34-35  3 SCR 59
R v Harrison, 2009 SCC 34 at para 20
There is no legal duty upon a person to identify himself to a police officer in every situation.
It is well understood that merely asking for ID alone does not amount to detention.
There should be a questioning that of suspected criminal activity that results in a "focused interrogation amounting to detention".
Where the obligation to answer questions, such as those related to identity, then the failure to do so may result in a charge of Obstruction of a Peace Officer under s. 129 of the Criminal Code.
The compelled attendance to the principal's office is not a detention.
Motor Vehicle stops
Random traffic check stops are prima facie violations of right to be free from arbitrary detention, however, have often been declared justifiable pursuant to s. 1 of the Charter. 
Investigating a Motor Vehicle Act violation does not permit the officer to take the detained person into the police vehicle even where safety may be a concern.
Random stops of persons for "reasons related to driving a car such as checking the driver's licence and insurance, the sobriety of the driver and the mechanical fitness of the vehicle"
Dual purposes in random traffic stops are permissible.
Random stop programs that are used to investigate for any number of offences, providing for a "comprehensive check for criminal activity", are flawed and cannot permit detention for any purpose at all.
- R v. Brookwell 2008 ABQB 545 at para. 29, citing R v. Orbanski & Elias 2005 SCC 37, at para. 31.
- R. v. Harder, 1989 CanLII 2857, 49 C.C.C. (3d) 565 (B.C.C.A.);
R. v. Greene,  N.J. No. 12 , 62 C.C.C. (3d) 344 (Nfld. C.A.)
- R. v. Hufsky, 1988 CanLII 72,  1 S.C.R. 621 ; R. v. Ladouceur, 1990 CanLII 108,  1 S.C.R. 1257 ; and R. v. Mellenthin, 1992 CanLII 50 (S.C.C.),  3 S.C.R. 615 ; R. v. Simpson (1993), 79 C.C.C. (3d) 482 (Ont. C.A.) 
- R. v. Timmer, 2011 ABQB 629
- R. v. Nolet, 2010 SCC 24 at 25
- R. v. Nolet, 2010 SCC 24 referencing R v Ladouceur 2002 SKCA 73
Rights Upon Detention
Right to be Informed of Reasons
- See also Rights upon Arrest
At point of detention the detainee must be immediately "advised, in clear and simple language, of the reasons for the detention."
A person can only exercise his right to counsel under s. 10(b) in a meaningful way if he knows the extent of his jeopardy.
The rights under s.10(b) have been met where the substance of what the accused can reasonably be supposed to understand in the context and circumstances of the case.
- Mann at para. 21
R. v. Kelly, (1985), 7 O.A.C. 46,  O.J. No. 2 at para. 14
- R. v. S.E.V., 2009 ABCA 108 (CanLII) at para. 22
R. v. Black, 1989 CanLII 75 (SCC),  2 S.C.R. 138, 50 C.C.C. (3d) 1 at para. 24
- R. v. Evans, 1991 CanLII 98 (SCC),  1 S.C.R. 869, 63 C.C.C. (3d) 289 at para. 35
R. v. S.E.V., 2009 ABCA 108 (CanLII) at para. 23