Anisah Hassan and Josh Stark are Toronto-based lawyers and graduates of the University of Toronto Faculty of Law.

Last month, the Supreme Court of Canada decided that police do not need a warrant to search the contents of your cellphone. In R v Fearon, a majority of the court decided that police can search the contents of your cellphone as long as the search is "truly incidental" to a lawful arrest and is tailored to the reason for the arrest.

This decision does not appreciate how technology has changed the privacy interests of Canadians. Smart phones have forever altered the way we use, store and relate to information. This has upended many of our intuitions about privacy. This is especially true for Millennials, who make greater use of smart phones and have a greater privacy interest in their contents.

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In 2013, 80 per cent of Millennials owned a smartphone, compared to 36 per cent of Canadian adults overall. We rely on our phones more than older Canadians and are more likely to take advantage of all they offer. For those who use their mobile phone as their primary computer, the privacy interest is even greater. Today, 1.3 million Canadians access the Internet only through their phone. U.S. studies show that among young people, minority populations and low-income adults, around 50 per cent say that their mobile phone is their primary Internet device. This is particularly distressing when we consider that these are the very people who are most likely to be arrested, most likely to be stopped and questioned by the police and are over-represented in our prisons. The people who are most likely to be subject to warrantless searches of their phones are also those with the greatest privacy interest in their contents.

Modern phones contain an astounding amount of private information. If a police officer searched our phones, he could access every digital conversation we've had since 2006. Like millions of Canadians, we use mobile financial software to track our expenses, investments and debt. Our phones contain most photographs we take and give access to every important document on our home computers through apps like Dropbox. If you use Grindr, or another LGBTQ dating app, an officer could discover your sexual orientation merely by viewing the home screen. Google automatically displays travel routes to frequently visited places, providing an officer our work address or the address of a significant other. Many apps record location information, providing a record of your movements over a period of weeks, months or years. Even if you don't use such an app, most smartphones automatically keep location data that can be easily extracted with equipment available to the police.

Imagine what it would have taken for police to access the same information in an era before smartphones. In the late 1970s – when most of the Supreme Court was our age – it would have been almost impossible. Police would have to follow you and record all your movements for months. They would need to copy years' worth of your mail, tap your phone and even record your conversations in public spaces in order to capture the incidental communication that Millennials conduct over text, e-mail or social networking. They would have to enter your home and copy your address book, your journal, your photo albums and your financial records. This is the information the majority decision grants to police without a warrant.

Thirty years ago, police would only have access to this information in extreme circumstances, because obtaining it required expensive and difficult surveillance operations. Now, those barriers are gone and the best remaining protections are legal ones, like warrants.

Although the majority requires that any search be tailored to the purpose of the arrest, this provides little meaningful protection. Substantial information is displayed automatically on the home screen, making it impossible for an officer to avoid. Regardless, all information on your phone is available if the arresting officer determines that it is relevant to the arrest. Had the court allowed police to search your home without a warrant, there would be little comfort in knowing that the search was restricted to anything in plain view, your mail and whatever else the arresting officer considers relevant.

We understand that cellphone searches are sometimes necessary to obtain important evidence. But the same is true of searching your home. The most invasive searches tend to be the most useful, precisely because of their invasiveness. The U.S. Supreme Court recently recognized this in a unanimous decision requiring a warrant for cellphone searches. As a society, we've decided that police need a warrant to search your home, barring exceptional circumstances. But the underlying assumption – that our homes, not our phones, contain our most private information – is increasingly untrue. Should police search our homes, we would not be alone among our generation were our first thought: "Oh god – is my phone there?"