When a building in New York recently caught fire and partially collapsed, injuring 30, many people's first instinct was to turn to social media. On Periscope, Twitter's livestreaming video app, users could watch in real time as first-responders arrived on the scene and closed down the street.

It's easy to see why services like Periscope — and its slightly older rival, Meerkat — are taking off. They let us experience viscerally — and anonymously — what's happening to other people as though we're behind the camera ourselves. The last generation of social media could only hint at that kind of engagement through short snippets of text and pretty pictures.

But as empowering as these apps are, expect them to grant even greater capabilities to law enforcement — who, through watching live videos of people screwing up, will gain an unprecedented ability to catch criminals in the act and gather embarrassing evidence of wrongdoing.

"There'll be thieves showing off their goods" on these services, said Stephen Balkam, president of the Family Online Safety Institute. "That's as stupid as it gets."

If you think that's far-fetched, you clearly haven't been introduced to the wealth of crazy that's already pervasive on Periscope and Meerkat. Vice has an exhaustive rundown of users broadcasting themselves smoking pot, driving cars and showing skin (or promising to do so). One recent stream I watched was simply pointed at the TV, where an episode of "Family Guy" appeared to be playing.

Many of these behaviors might be considered illegal in some jurisdictions. Unless you're in Colorado, Alaska, the nation's capital or a couple other places, it's still against the law to use marijuana. Rebroadcasting a TV show you're watching? That's not much different from walking into a movie theater with Google Glass, a decision that can get you thrown out — or worse.

For years, authorities have used information from Facebook, Twitter and other social networks to apprehend criminals or build a case against them. We know this, because the companies' own transparency reports say so. Nor are we unaccustomed to learning about someone's life on video. YouTube already lets us do this. Chatroulette even enabled that in real time.

But Chatroulette also opened up the video stream both ways, connecting two people over webcams. What makes Periscope and Meerkat such a leap forward for cops is that they can open up a livestream without anyone else knowing. In that respect, they're just like all the other lurkers. The difference is that these lurkers can arrest you.

"Chatroulette's been out there quite a while, but they were very much on the margins," said Balkam. "Meerkat and Periscope bring this into the mainstream."

SWAT teams aren't going to descend on you if you're doing nothing wrong. And even if you are breaking the law, the authorities have to find your stream and open it to know. Then they have to find a way to save these ephemeral videos so that they can produce them in court later. All seemingly high bars.

Still, it's unclear how much, if at all, these types of services are subject to law enforcement demands. Meerkat does not store videos on its servers and hasn't received any government warrants or subpoenas to date, said Ryan Cooley, Meerkat's community director. A spokesperson for Periscope did not immediately respond to a request for comment.

All this suggests it may be more difficult for authorities to use livestreaming services for forensic purposes, even if the apps leave the door open to real-time surveillance.

It's easy to scoff at the dumb people who commit serious crimes and then broadcast them. This isn't really about them. It's about the poor, ordinary people who transgress but don't know they've done it — or who don't think it's a big deal. Or people who haven't actually broken the law but that for whatever reason, their livestream simply makes it look as though they have. Video is a powerful way to document cases of wrongdoing, real or imagined.

What's the role of Periscope and Meerkat in all this? As we've seen with Facebook and Twitter, individual users are generally responsible for their own actions on the platform. It's merely up to the companies to police their own content policies (Here are the ones for Periscope and Meerkat.)

But as livestreaming apps break down the wall between our social media personae and our real, physical lives, policing content becomes a much trickier proposition. With livestreaming apps, cutting off videos that feature illicit or abusive behavior — stuff that, on any other platform, would be considered merely "content" — becomes a much more intrusive way of regulating people's actual lives offline.