It’s been some time now, but the Supreme Court’s decision in R v Mills, 2019 SCC 22, is worth a comment. This is yet another case in which the Court had to address the application of the right, protected by section 8 of the Canadian Charter of Rights and Freedoms, “to be secure against unreasonable search or seizure” to new-ish technologies. These cases often divide the court, but seldom as much as Mills, where Justice Brown signs a leading opinion for himself and Justices Abella and Gascon; Justice Karakatsanis has a concurrence to which the Chief Justice signs on; Justice Moldaver agrees with Justice Brown (whose opinion is thus, in effect, a majority one) and Justice Karakatsanis; and Justice Martin also concurs, but on grounds quite different from her colleagues’.
The issue in Mills had to do with the privacy interests that one might have in one’s online conversations. Justice Brown usefully sets out the facts. The case developed from
a sting conducted by a police officer, who posed online as a 14-year-old girl, with the intent of catching Internet child lurers. Over two months, [Mr.] Mills sent several messages, using Facebook and Hotmail. Eventually, he was arrested in a public park where he had arranged a meeting with the “child”, and was charged … with luring a child via the Internet. The entire operation occurred without prior judicial authorization. Using a screen capture software, the police introduced a record of the emails and messages as evidence at trial. [2-3; paragraph break removed]
Mr. Mills alleged a violation of his section 8 rights, and sought to have the evidence excluded. To decide whether his rights were indeed at stake, the Court must determine whether he had a subjective expectation of privacy in the subject-matter of the alleged search or seizure, and whether this expectation was objective. As usual, it is this last question ― as Justice Brown notes, a “normative question about when Canadians ought to expect privacy, given the applicable considerations” [20; emphasis Justice Brown’s] ― that causes difficulty here.
For Justice Brown, the key to the case is to be found in “the nature of the investigative technique used by police, and the nature of the relationship between the communicants [sic].”  In Justice Brown’s view, in light of children’s special vulnerability, “adults cannot reasonably expect privacy online with children they do not know”  ― or persons whom they believe to be such children. The relationship here was one between strangers ― since the purported child was in fact a creature of the police ― and the police, obviously, knew this before they started looking at the communications between that “child” and the accused. Unlike in cases where the police intercept or obtain communications between individuals the nature of whose relationship to one another they do not know, they can be certain of breaching no one’s reasonable privacy interests, and so do not need judicial authorization.
Justice Karakatsanis also finds that Mr. Mills could not reasonably expect the messages at issue to remain private. But in her view, that is because the state, acting through the undercover police officer, was the other party to the conversation, and one cannot expect one’s messages to remain private from the party to whom one deliberately sends them. Police officers do not infringe anyone’s privacy rights be speaking to them, even when they are undercover. Conversations via online messaging or email are no different. While the surreptitious recording of what is ostensibly a purely oral conversation makes what was meant to be ephemeral permanent and so has privacy implications, this issue does not arise when writing was the originally chosen medium of communication. Justice Karakatsanis alludes to concerns raised by interveners about police officers posing as persons to whom individuals might want to confide personal information, but decides that they need not be addressed in this case.
Justice Martin takes a different view of the privacy concerns raised by Mr. Mills. For her, the case raises the issue of “whether the state should be permitted to conduct warrantless surveillance of private, electronic communications, or whether that state surveillance should be regulated”.  The answer is that “[i]f the police wish to acquire a record of those communications, … such investigative activities must be regulated. The precise nature of such regulation is best left to Parliament”. 
Like Justice Karakatsanis, Justice Martin refers to the distinction between transient and permanent communications. But to her mind, the salient point here is that the distinction is being erased:
Online communications are inherently recorded. Where the intrusive technology used to be in the hands of the state, it is now in our back pockets. … [T]he electronic communications in the case at bar constituted both the conversation and the surreptitious electronic recording of that conversation. [86; 93]
Justice Martin endorses the concerns expressed in cases going back to the 1970s that people will, in effect, self-censor if they know that their words may be recorded and publicized. Indeed, Justice Martin worries about government “subjecting the public to surreptitious electronic surveillance on a mass scale”.  And since technology makes the existence of recordings inevitable, there need to be robust protections for their privacy. Nor can the state get around these protections by impersonating someone to whom a citizen may wish to speak privately; if it does so, the fact that the recorded words were addressed to the state agent is beside the point. On the contrary, “[t]he ability to fabricate alternative identities has never been more possible [sic] than it is now”,  and this reinforces the need for safeguards against the state taking advantage of this ability to elicit private information from citizens.
Justice Martin is also unimpressed by Justice Brown’s approach to the case. She thinks it inconsistent with the usual, content-neutral approach to section 8 cases. More importantly, saying that communications occurring between particular types of people ― such as those between an adult and a child who is a stranger to him or her ― are necessarily excluded from the scope of section 8 is inconsistent with that provision’s text, which guarantees rights to “everyone”, and
seeks to put courts in the business of evaluating the Canadian public’s personal relationships with a view to deciding which among them deserve Charter protection … Judicial (dis)approbation of an accused’s lifestyle has no place in the s[ection] 8 privacy analysis. 
Ultimately, however, Justice Martin finds that while the police breached the accused’s Charter right to be secure against unreasonable search and seizure, admitting the evidence they collected would not bring the administration of justice into disrepute. Thus she agrees with her colleagues about the result of the case, if little else. (As previously discussed here by Peter McCormick, Mills will count as a unanimous case in the Supreme Court’s statistics. It is anything but!)
To a striking degree, Mills illustrates Orin Kerr’s “equilibrium-adjustment theory” of constitutional protections against unreasonable search and seizure. In a nutshell, this theory posits that “[w]hen new tools and new practices threaten to expand or contract police power in a significant way” as compared to a (hypothetical) “year-zero” balance, “courts adjust the level of [privacy] protection to try to restore the prior equilibrium”. (480) Here, the tools and practices ― available both to the police and to the citizens (criminal and law-abiding alike) are online communication platforms that combine possible anonymity with the recording of conversations (and so, as just noted, the erasure of the demarcation between the spoken and the written word).
As equilibrium-adjustment theory predicts, Justices Brown, Karakatsanis, and Martin all frame their reasons as means to preserve or restore a balance of privacy that these developments threaten to disrupt. Thus Justice Brown insists that the means used by the police in this case “did not significantly reduce the sphere of privacy enjoyed by Canadians”.  For her part, Justice Martin argues that the “Court must identify the privacy interest [previous] cases sought to protect and ensure that it remains protected as the communication environment evolves”.  Justice Karakatsanis is perhaps a little less explicit about her own effort at equilibrium adjustment, by her insistence that written communications have not, in the past, been treated in the same way as oral conversations, and should not be so treated now is also in that vein, as is her concern that “[t]he alternative conclusion would significantly and negatively impact police undercover operations, including those conducted electronically”. 
But while all the judges in Mills agree on the importance of preserving the balance between privacy and the ability of police to investigate crime, it is not so clear where exactly that equilibrium really was. At equilibrium, was it the case that adults had no privacy rights in their relationships with children who were strangers to them, Justice Brown suggests? Or that the written word was not private in the way the spoke word was, as Justice Karakatsanis argues? Or, on the contrary, that all relationships, regardless of the parties’ status, and all conversations, regardless of the means used to carry them out, were entitled to privacy protections, as Justice Martin suggests?
Justice Brown’s attempt at defining equilibrium does not persuade me. As Steven Penney wrote in his (rather timelier than mine) comment on Mills on the University of Alberta Faculty of Law Blog, it is difficult, if not impossible, to tell when two persons are “strangers” to one another:
What degree of familiarity with an online persona is required before he or she ceases to become a stranger? Is it necessary to have met the person face-to-face in the offline world? Or is it enough to have had prior oral conversations (whether audio-only or video chats) online? And what, if any, degree of identity verification is required?
Meanwhile, the concept of “children” seems perfectly well-defined, in this context, as people under the age of 18, but this clarity might not be all it seems (because people lie about their age), and comes with its own set of problems. Are close-in-age relationships different? What about relationships between two minors? Why, indeed, draw a hard line at 18, especially outside the context of sexual crimes? Alternatively, must investigations of sexual crimes be treated differently than those of, say, terrorism?
One is tempted to suspect (Professor Penney, I think, hints at this too) that Justice Brown was looking for a very narrow basis on which to resolve this case. But the trouble is that an artificially narrow decision in a difficult case risks both being unprincipled and simply kicking the can down the road. Justice Brown’s opinion is in serious jeopardy on both these counts; indeed, I am inclined to declare it guilty on the second, even if a reasonable doubt might exist as to the first.
But what about the disagreement between Justices Karakatsanis and Martin? Perhaps this disagreement is the latest ― and probably not the last ― manifestation of a recurrent problem in cases about the application of section 8 of the Charter, which I described here when commenting on the Supreme Court’s decision in R v Marakah, 2017 SCC 59,  2 SCR 608, a case that considered the privacy of a text messaging conversation that one of the parties handed over to the police:
A number of legal issues arising out of new technologies, broadly speaking, have to do with the erasure of the once-clear line between the spoken and the written word. The former was (usually) spontaneous and fleeting; the latter (relatively) deliberate and permanent. But electronic communications combine spontaneity and permanence in a way to which many of us are still only getting used and with which the legal system, unsurprisingly, struggles.
In Marakah, a majority of the court (which included Justice Karakatsanis) held that a reasonable expectation of privacy in the conversation existed, so that the police could not look at it without prior authorization, even with the consent of one of the parties. I think that decision could also be understood as an attempt at equilibrium-adjustment, intended to preserve the previously undoubted privacy of the exact content of personal conversations. Professor Penney argues that Justice Karakatsanis now tries attempts to “effectively overturn” Marakah.
But I’m not sure that this is fair, or that the problem of the newfound permanence of conversations is really what is driving the disagreement between Justices Karakatsanis and Martin in Mills. Justice Karakatsanis does not deny that (in Professor Penney’s words) “Marakah … puts automatically recorded text conversations on the same plane as surreptitiously recorded oral ones”. Rather, she wants to hold on to a distinction that, as I see it, Marakah did not foreclose: that between the state obtaining, by whatever means, a conversation to which it was not a party (as it had done in Marakah), and that between the state itself in effect being a party to the conversation. In the latter case, Justice Karakatsanis argues, “[t]he fact that the conversation took place in a written form … does not transform it into a search or seizure”.  In other words, for Justice Karakatsanis, as for the Marakah majority, oral and electronic conversations are alike; those that involve a state representative and those that do not are not.
And, so far as this goes, I tentatively think that Justice Karakatsanis is right: considered by itself, the (electronic) conversation between a suspect and an undercover police officer in Mills is not a meaningfully greater intrusion on the suspect’s privacy than a conversation with an in-person informant would have been. Of course,there is a word-for-word record of that conversation. But, as Justice Karakatsanis says, the suspect knows this in advance. It’s all good and well to proclaim that the “reasonable expectation of privacy” standard is normative, not descriptive; it’s about what people ought to expect, not what they actually expect. But the standard cannot be entirely unmoored from the facts and, in particular, from the fact that we know and indeed use tools (such as search functions) that rely on the fact that the words of our conversations are recorded in real time.
That said, there is also a different equilibrium-adjustment issue in Mills, and it is this issue which, I think, really drives the disagreement between Justices Karakatsanis and Martin: namely, whether the ability of the police to engage in online undercover surveillance will radically expand the use of this investigative technique. Justice Martin think that it will, and so wants to forestall this expansion of police power. She envisions “mass scale” surveillance, previously “inconceivable … due to the practical resource constraints of [in-person] undercover police work”  and because of the much greater variety of fictitious personas investigators might be able to adopt online. Justice Karakatsanis is skeptical about this (as is Justice Brown). It is very difficult to say who is right here. Justice Martin, I think is speculating about the future prospects of mass surveillance; for now, at least, I don’t see the prospect of pervasive police stings using fake online personas as anything more than a dystopian fantasy, albeit, to be sure, not an entirely implausible one. And, in fairness, Justices Karakatsanis and Brown are speculating too, hoping that this dystopia does not come to pass, or at least that its development, should it begin in the earnest, will be able to be checked then.
So let me finish with a thought on one way to help prevent the dystopian future. It will perhaps seem naïve, but I think it is actually important. There are two ways to reduce the odds of police investigations unduly intruding on citizens’ lives. One is to constrain investigations once they are launched by limiting the use of certain techniques, requiring warrants, etc. Section 8 of the Charter, and equivalent provisions of other constitutional instruments, do this but, as cases such as Mills illustrate, constructing good doctrine in such cases is not easy. The other way to keep police in check is to have fewer crimes for them to investigate in the first place. As Justice Gorsuch, of the US Supreme Court, observed just a couple of days ago in Nieves v Bartlett,
History shows that governments sometimes seek to regulate our lives finely, acutely, thoroughly, and exhaustively. In our own time and place, criminal laws have grown so exuberantly and come to cover so much previously innocent conduct that almost anyone can be arrested for something. (Slip op. 1-2; that’s pp. 24-25 of the PDF)
And of course, before one can be arrested, one can be investigated. Perhaps the Canadian situation is not as bad as the American one (I don’t know enough to tell) but, if so, we must work to keep it that way. And here, the Charter ― just like its counterparts elsewhere ― is not going to help us. Only sustained political opposition to overcriminalization ― and, ideally, sustainted political support for decriminalization of a great many things currently considered criminal ― will do the trick.