When neighbors Hugh Bartlett and Caria Tomczykowska moved to Oakland's Oakmore District years ago, they never dreamed they'd be considering surveillance cameras.
"We're frustrated by the reduction in the police force that's happened and that's definitely contributed to crime, I think," said Bartlett.
"People who commit the crimes are getting much more brazen, the fact that they feel they can go ahead and kick in doors, whether there are people there or not is not a good thing," said Tomczykowska.
So after one especially violent robbery, neighbors began to organize using a new social network called Nextdoor.
"Nextdoor is a private social network for your neighborhood," said Nextdoor CEO Nirav Tolia.
Tolia says while we're busy reaching out to friends around the world on Facebook, we might be ignoring our neighbors.
"You see them when you take your dog out for a walk, you see them when you're coming in and out of your garage, but you don't know their names. Nextdoor makes it easy for you to get to know them, and once you have a critical mass of neighbors that you know, you can start to solve problems together," said Tolia.
Nextdoor's defining feature is that it requires you to prove you actually live in the neighborhood before you can see or post messages. You have to answer a home phone call or get a postcard in the mail with a special code.
"When you're talking about things related to your home, your address, where your children go to school, it's very important to be able to trust the people that you're communicating with," said Tolia.
You can post about anything such as something you lost or a good local doctor, but neighbors say one of the best uses is crime prevention.
"I mean literally within minutes we all know what is going on or that there's a suspicious car in the neighborhood," said Tomczykowska.
Nextdoor's public safety value was really put to the test in Menlo Park a couple of months ago. That's when police descended on a quiet neighborhood, looking for two armed suspects.
"My husband is home with our 2-year-old daughter. He sees a police officer's car just zooming, to say the least, down the street," said Menlo Park Nextdoor user Farah Shaikh.
Shaikh says her husband used Nextdoor to send out a text message alert. Neighbors stayed in their homes and shared what they knew.
"Pictures being posted, again, the live, the real time updates of what was happening was I think the most important factor of it all," said Shaikh.
Police departments are taking note. Belmont police used Nextdoor to track down and arrest a man who was driving around exposing himself.
"We put the alert out over Nextdoor and one of the neighbors in that neighborhood communicated back to us that he might have the suspect vehicle and the suspect on his home security camera," said Belmont Police Lt. Patrick Halleran.
Stories like those have earned Nextdoor the attention of Silicon Valley investors to the tune of $40 million.
Venturebeat writer Rebecca Grant explains why it's a good bet. She said, "This is a company where even if my mother hasn't heard of it, I explain it to her and she totally gets it."
They'll likely use all that money to expand, she says.
"They were contacted by a city councilman in Barcelona about whether they'll be able to set something up in Europe," said Grant.
But Barcelona hardly matters to Bartlett and Tomczykowska -- two neighbors who didn't know each other until they joined Nextdoor.
"It really has fostered a positive sense of community in the neighborhood. I'm glad it's here," said Bartlett.