Without doubt, one of the most consequential social changes of the past decade is how much information we choose to share publicly about our lives.

Facebook, Twitter, Pinterest, and blogs are some of the drivers of that change, of course.

But now millions of people also carry a smart phone in their pocket or purse that makes sharing every moment, including their physical location, easy to do.

Relatively few of us would choose to share everything with everybody, of course, and that’s where the mobile (iOS and android) social network Path comes in. 

“Path is really designed to be a highly personal social network where you share your life with the most important people in your life,” says Nate Johnson, the company’s VP of marketing. “We are part of the next wave of social networks, which are contextual social networks.”

So what do people post on Path?

“The stuff people share on Path is different from on Facebook & Twitter. We call them ‘moments.’ It’s almost like you’re living a person’s life with them, sharing the personal and intimate things. Photos, videos, music, books, when you go to sleep, and when you wake up.”

In fact, Johnson says, “sleep moments” are the third-most shared item on Path.

One way to use Path is as a "smart journal," a journal that’s with you everywhere you go, that can post entries without your effort, combining photo, video, music lists, people, places, and text, for your loved ones to stay in closer touch with you throughout your day.

An option called Automatic enables Path to learn about you as you go about your daily routine. With it, you can choose to have your journal automatically updated with stories about your life — “a journal that writes itself,” is how the company describes it.

As for the average number of people Path users share with, Johnson says the company allows up to 150, but most people top out in the 30-40 range.

“Our limit of 150 is based on academic research that the human brain is incapable of having more than 150 meaningful relationships at any one time. This goes way back, in fact, it is the size a tribe reached when they tended to split into new groups.”

When Path launched in late 2010, the initial limit was 50, but user feedback indicated that people needed more “space” to choose their closest friends and family members to share with – thus the decision to increase the limit to 150.

One of Path’s key team members, unusual for a startup, is a writer, Leigh Lucas, who serves as the “voice” of the service interjects personality into the app.

“People share mundane things but they are important because they add up to the story of their day,” she explains. “So I write hundreds of options that randomly post when you choose, for example, to share that you are going to sleep. My job is to help them post a moment that tells a good story. I like comics, and sounds, so there might be a light snoring sounds that may post. And if you don’t go to sleep until 2 a.m., it might say ‘luckily you’re thousands of miles from Transylvania.’”

To date some three million users have posted over three billion moments to Path, which is available in 17 languages with a global user base split roughly 50-50 in the U.S. and overseas.

The service is free, and contains no advertising. The company envisions charging for premium options, the first of which are specialized lenses and editing options for the high-res camera built into Path’s app that cost $0.99 each.

And if sharing everything all the time seems over the top, Path allows you to set your own limits. “In the settings you can keep moments just to yourself with the lock button,” notes Johnson. “Control is important to our users. You can always turn off location information. Privacy is a key tenant of our service.”