It's a relatively secretive piece of technology. So secretive that authorities don't even like to admit they use it. But the police are now using it to gather data from cellphones in Canadian cities. What can they do with that data? Depends on who you ask. Should you be worried? They say no, and privacy experts disagree—so in other words, it's another story about what we should expect when we walk around in public.

What are they collecting? How does it help solve crimes? What rights does the public have to their smartphones data signature? What's the logical extension of increased use of this technology? And, for the crimes it's supposed to solve, does it work?

GUEST: Kate Allen, Science and Technology reporter, Toronto Star