What is Signal? Signal is a messaging app, just like WhatsApp or iMessage or Facebook Messenger , but one that's geared towards privacy and security rather than cute emoji stickers. In fact, so good are its security measures that even Edward Snowden recommends it —and he should know which apps are the best for stopping unwanted snooping. Signal is free to use and available for Android , iOS , and Chrome (a browser extension that links with your phone), and alongside the extra security protocols, it includes all of the basic messaging tools you're going to need, including read receipts, emoji support, group chats, and voice and video calls. As on WhatsApp, Signal uses your mobile number to identify you to your contacts, so there are no new usernames or passwords to remember, and you can dive straight in. On Android, you can also use Signal to send normal SMS and MMS messages to contacts who don't have the app installed, but these messages won't