(CNN) -- Back when Facebook only had millions of users instead of a billion, before Timeline and the bungled IPO and outrage over privacy issues, people "poked" each other on the social network. The poke, which is still around but rarely used, is a minimalistic form of communication -- the digital equivalent of a head nod or wink.
Now the social network has expanded the poke into a standalone iOS app, which was released on Friday. The simple free app, called Facebook Poke, allows you to send fleeting messages, pokes, photos and 10-second videos to Facebook friends. The messages expire after a set period of time, from 1 to 10 seconds, and cannot be retrieved by either party again. This makes the app perfect for sending salacious images without leaving a trail.
"With the Poke app, you can poke or send a message, photo, or video to Facebook friends to share what you're up to in a lightweight way," says Facebook in a blog post announcing the new app.
When you open the app, you can choose from a set of icons at the bottom of the screen to send a poke, type a 120-character message, open the camera to snap a picture (you cannot choose an existing photo from your camera roll, but you can add fun doodles or text on top of the picture you do take), or shoot a 10-second video. Decide how long you want the other person to see your message or photo (1, 3, 5 or 10 seconds), add a location if you like, then choose one or more of your Facebook friends from the list and hit send.
To view a message, tap and hold until the little countdown clock in the corner runs down, and the message is gone forever. You can see a list of who send you messages, but not view them again.
The app Poke shamelessly imitates is Snapchat, a photo and video-sharing service that has surged in popularity over the past year year. It's no mystery why Facebook is jumping on the temporary message bandwagon. Snapchat says it has millions of users who send around 50 million messages a day. It is also popular with the highly valuable younger age group, though it doesn't currently have ads or any other way of making money off of its service. The Facebook Poke app is also ad-free for the time being.
The allure of self-destructing messages is that they are unlikely to be seen by anyone other than the recipient, or to resurface during a campaign for public office. Snapchat has earned a reputation as a tool for sending risqué photos, though its also handy for funny or silly images for friends.
Because of the private nature of these messages, the apps have built-in safeguards. The only way to keep a copy of a photo on these apps is to take a screenshot with your phone. Both Poke and Snapchat warn the sender when the recipient has grabbed a screenshot of their message.
Facebook seems keenly aware of how the Poke app will be used by most people.
"If you ever see something you're uncomfortable with, you can click the gear menu and report it," says the company in the post. In the app's help center there are instructions for what to do when someone takes a screenshot against your will. That section helpfully links to a post on what to do when an adult is making you uncomfortable, and another on what to do when someone requests nude photos.
The app is Facebook's fifth iOS app, joining the main Facebook app, Facebook Messenger and Facebook Camera.