Encrypted messaging app Signal has been around since 2015, gaining popularity among political activists of all stripes because of its secure and private messaging system. More recently, a mass exodus from Facebook-owned WhatsApp, fueled by its demand for new terms of service and increased information sharing with its corporate parent, has boosted Signal as a major alternative for many new users. If you’re unfamiliar with the app and how it works, we break down what Signal is and how to use it.

Signal Private Messenger is available for free worldwide for both iOS and Android and allows its millions of users to send texts, videos, and files, make voice and video calls, and shield your location using end-to-end encryption. It also has a desktop version for Mac, Windows, and Linux. It looks and works like any other messaging app and uses your name, phone number, and address book to look up and contact people you know. Messages are decipherable only by participants in the conversation. 

End-to-end encryption, enabled in Signal by default, is powered by the open-source Signal Protocol that secures both conversations and encrypts metadata as well so that no one knows the content or the participants in communication. Signal lets you choose custom alerts for each contact or disable sound completely. Built-in image-editing features let you sketch, crop, blur, and flip photos. You can read receipts, use stickers, and approve or block messages from specific signal users.

Signal keeps people’s messages hidden even if their phones are stolen, hacked, or confiscated by police. If unknown third parties gain access, your messages appear in a code that they would be unable to decipher. Because Signal is also an open-source, peer-reviewed app run by an independent nonprofit funded by grants and donations, anyone with knowledge and expertise can review Signal’s program for flaws.

Signal development is financially supported by users so it can operate without advertisers or trackers. That’s the difference between Signal and WhatsApp and Facebook Messenger, which also boast end-to-end encryption messaging. Unlike Signal, these apps still collect personal data for advertising purposes. Both Telegram and Apple’s iMessage are also end-to-end encrypted, but Telegram’s encryption is not enabled by default but rather via a secret chat option between two users (not groups) bypassing the cloud. Apple’s iMessage is only encrypted if both parties are using an iPhone. With Signal, encrypted conversations can only occur when both or all participants use Signal.

Mobile signal users must be running Android 4.4 or later or iOS 11.1 or later. As part of the setup, you must enter your phone number and a code sent to your phone number to verify your identity. You must also create a four-digit PIN code for security verification, but you can disable it later if you prefer. Once you’re set up, you can freely send and receive messages to and from other Signal users. Signal syncs with your phone’s contact list to show which of your contacts also use the service. 

One handy feature is the option to delete individual conversations after a designated amount of time. To enable this feature, just click on a user’s profile and make sure that Disappearing Messages is toggled on. You can make Signal your default messaging app on Android via Settings > Apps & Notifications > Advanced > Default Apps > SMS App > Signal. The iPhone does not allow you to choose a third-party default messaging app. To operate Signal from desktop to mobile, where messages are synchronized with Signal on your mobile phone, you need Windows 64-bit 7, 8, 8.1 or 10, MacOS 10.10 and above, or Linux 64-bit supporting APT, like Ubuntu or Debian.

Examples below are derived from an LG V40 ThinQ running Android 10 and an iPhone 12 Mini running iOS 14.3.

While Signal requires a phone number, you can use a Google Voice number if you prefer not to use your real one.

Your Signal profile — name and picture that you set up with the app — is encrypted, but you can recover it via your PIN. Profiles are mandatory so your contacts know who is messaging them, though your ID can be as cryptic as only a first name, nickname, a single character, or an emoji.

Once everything is set up, it’s time to start sending messages via Signal. The process is virtually identical on both iOS and Android.

Signal isn’t just for messages; you can make encrypted phone calls with the app as well.

Signal can send photos and videos and even blur them for extra privacy. If you shoot a photo within the Signal app, it does not automatically save it to your gallery or camera roll. You can limit the amount of time a photo or video remains visible on the recipient’s device and add decorative stickers and emoji.

Signal lets you manage your message notifications in a granular way to ensure  privacy. Here’s how to do it.

Another Signal-based screen-lock feature requires your password, FaceID, or TouchID to view messages. On iOS, tap your Profile > Privacy > Screen Lock and toggle it on. With Android, there’s a Screen Lock Inactivity Timeout control that lets you activate the feature over time. Enabling Screen Security prevents Signal contents from visibility on your app switcher. On Android, it also prevents screenshots of Signal activities on your device.