Signal: Open Source Data Security & Privacy

What is Signal?

What it is

Signal Android is a secure messaging application for Android devices that delivers private communication via end-to-end encryption. Developed by Signal Messenger, LLC, it operates within the broader Signal ecosystem, which includes official iOS and desktop clients. The app uses mobile data or Wi-Fi to send and receive encrypted messages, voice calls, and video calls without relying on traditional SMS or telephony infrastructure.

It solves the problem of insecure communication by ensuring all content—messages, calls, files—is encrypted from sender to recipient using the Signal Protocol, a rigorously audited encryption standard. Unlike many mainstream messengers, Signal does not store message content on servers, nor does it collect user metadata for advertising or profiling. This makes it suitable for users requiring strong privacy guarantees, including journalists, activists, and everyday users concerned about surveillance or data exploitation.

Key capabilities

End-to-end encryption for all messages, calls, and media using the Signal Protocol
HD voice and video calling with encryption and low-latency audio/video codecs
Disappearing messages with configurable timers (from 1 hour to 1 year)
Screen security to prevent screenshots and background app previews
Group messaging and calling with up to 1000 participants, including group admin controls
Profile avatar and name sharing via encrypted server-stored profiles
Open-source codebase with public auditability and AGPL-3.0 licensing

Who uses it and how

Journalists and human rights defenders use Signal for confidential source communication and coordination in high-risk environments
General users rely on it as a default messaging app to replace SMS or carrier-based apps due to privacy concerns
Organizations deploy Signal internally for secure team communication, often using group features and disappearing messages for sensitive workflows

Getting started

Install via Google Play Store (package org.thoughtcrime.securesms) or download APK directly from signal.org/android/apk/. Beta releases are available through the Play Store’s beta testing program. No account creation is required—sign-up uses phone number verification only.

When to use it — and when not to

Signal is ideal when end-to-end encryption, transparency, and minimal data retention are priorities. It replaces paid enterprise secure messaging platforms but requires users to manage their own device backups and recovery (no cloud backup integration). It does not support federated deployment or self-hosted infrastructure; all users connect to Signal’s centralized, non-profit-operated servers. Users in regions with strict cryptography regulations must verify local compliance before deployment.

project readme (upstream, from github) — read inline

Signal Android

Signal is a simple, powerful, and secure messenger that uses your phone's data connection (WiFi/4G/5G) to communicate securely.

Millions of people use Signal every day for free and instantaneous communication anywhere in the world. Send and receive high-fidelity messages, participate in HD voice/video calls, and explore a growing set of new features that help you stay connected.

Signal’s advanced privacy-preserving technology is always enabled, so you can focus on sharing the moments that matter with the people who matter to you.

Currently available on the Play Store and signal.org.

Also available on iOS and Desktop.

Contributing Bug Reports

We use GitHub for bug tracking. Please search the existing issues for your bug and create a new one if the issue is not yet tracked!

https://github.com/signalapp/Signal-Android/issues

Joining the Beta

Want to live life on the bleeding edge and help out with testing?

You can subscribe to Signal Android Beta releases here: https://play.google.com/apps/testing/org.thoughtcrime.securesms

If you're interested in a life of peace and tranquility, stick with the standard releases.

Contributing Translations

Interested in helping translate Signal? Contribute here:

https://community.signalusers.org/c/translation-feedback/

Contributing Code

If you're new to the Signal codebase, we recommend going through our issues and picking out a simple bug to fix in order to get yourself familiar. Also please have a look at the CONTRIBUTING.md, that might answer some of your questions.

For larger changes and feature ideas, we ask that you propose it on the unofficial Community Forum for a high-level discussion with the wider community before implementation.

Contributing Ideas

Have something you want to say about Signal projects or want to be part of the conversation? Get involved in the community forum.

Help

Support

For troubleshooting and questions, please visit our support center!

https://support.signal.org/

Documentation

Looking for documentation? Check out the wiki!

https://github.com/signalapp/Signal-Android/wiki

Legal things

Cryptography Notice

This distribution includes cryptographic software. The country in which you currently reside may have restrictions on the import, possession, use, and/or re-export to another country, of encryption software. BEFORE using any encryption software, please check your country's laws, regulations and policies concerning the import, possession, or use, and re-export of encryption software, to see if this is permitted. See for more information.

The U.S. Government Department of Commerce, Bureau of Industry and Security (BIS), has classified this software as Export Commodity Control Number (ECCN) 5D002.C.1, which includes information security software using or performing cryptographic functions with asymmetric algorithms. The form and manner of this distribution makes it eligible for export under the License Exception ENC Technology Software Unrestricted (TSU) exception (see the BIS Export Administration Regulations, Section 740.13) for both object code and source code.

License

Licensed under the GNU AGPLv3: https://www.gnu.org/licenses/agpl-3.0.html

Google Play and the Google Play logo are trademarks of Google LLC.

Frequently asked questions

Is Signal free to use?

Signal is open source under the AGPL-3.0 licence. There is no licence fee and no seat count — you can self-host it or, where the project offers one, pay a vendor for a managed version instead.

What does Signal do?

Private messaging with end-to-end encryption

What is Signal written in?

Signal is primarily written in Kotlin. Its source is publicly available at https://github.com/signalapp/Signal-Android, and it has 29,352 GitHub stars.