It secures all communications with end-to-end encryption. Signal uses mobile telephone numbers as identifier for users. Registration for desktop use requires an iOS or Android device. Signal is also distributed for iOS and desktop programs for Windows, macOS, and Linux. The official Android app generally uses the proprietary Google Play Services, although it is designed to work without them. Its mobile clients are published under the GPL-3.0-only license, while the desktop client and server are published under the AGPL-3.0-only license.

Signal's software is free and open-source. It is developed by the non-profit Signal Foundation and its subsidiary, Signal Messenger LLC. The application uses a centralized computing architecture, and is cross-platform software. Communication may be one-to-one between users, or for group messaging. The instant messaging function includes sending text, voice notes, images, videos, and other files. Signal is an encrypted messaging service for instant messaging, voice, and video calls.

Signal private app