Signal (messaging app)
Also known as: Signal, Signal app, Signal Messenger, Signal Private Messenger
Signal is a free messaging app for texts, voice and video calls, and group chats, with end-to-end encryption on by default for everything.
It's run by the non-profit Signal Foundation and collects very little data about its users. Its encryption design, the Signal Protocol, is also used by WhatsApp and others. Signal supports disappearing messages, usernames that hide phone numbers, and post-quantum encryption. While Signal is widely recommended by security experts, encryption doesn't protect against adding the wrong person to a chat or a compromised phone.
Signal (messaging app), explained at three levels
At home
Signal is like sending letters in locked boxes where only the recipient holds the key. Your phone scrambles each message before it leaves, and only the other person's phone can unscramble it. Signal's servers carry the boxes but cannot open them, and Signal keeps very little record of who wrote to whom. Calls, photos and group chats are protected the same way.
At work
Signal is a free messaging app run by a non-profit, with end-to-end encryption on by default for messages, calls and group chats. Only the people in a conversation can read it, not Signal or anyone else. Businesses care because it protects sensitive conversations well, but messages live only on devices, so it may not meet record-keeping rules in regulated industries or the public sector.
At home
Signal encrypts every message on your phone before it leaves, using keys that only the people in the conversation hold. Its servers relay scrambled messages they cannot read. The Signal Protocol also changes keys constantly as you chat, so even if one key were stolen, it would unlock very little. Signal goes further than most apps by minimizing what it stores about you, such as who you talk to, using a technique called sealed sender to hide the sender from its own servers.
At work
Signal is run by a non-profit foundation and its code is open source. Its protocol is also used by WhatsApp and Google Messages for encrypted chats. Messages are stored only on devices, not servers, so they cannot be retrieved for audits or legal discovery. That conflicts with record-keeping obligations in regulated industries, such as finance, and with public sector rules for official communications, so organizations must decide whether it is approved for business use.
At home
Signal's encryption is very strong, so problems usually come from people, not maths. Adding the wrong contact to a group, as happened when a journalist was added to a US government Signal chat in 2025, exposes every message from then on. Screenshots and unlocked phones bypass encryption entirely. In my view, the biggest Signal risk is adding the wrong person, not broken encryption, so check who is in a group before sharing sensitive things.
At work
Set policies on which messaging apps can be used for business, considering record retention, freedom of information obligations and legal holds, since disappearing messages may destroy records that must be kept. For high-risk contacts, verify safety numbers in person or by another channel. Secure devices with strong passcodes and current updates, because end-to-end encryption does not protect an unlocked or compromised phone. Approved archiving tools exist for some regulated sectors.
Real-world examples
At home
Lena's family switched their group chat to Signal for privacy. Her grandmother found it as easy to use as regular texting.
At work
Jerome's Regina MSP helped a journalist client set up Signal with disappearing messages and registration lock to protect sources.
How it compares
| feature | Signal (messaging app) | |
|---|---|---|
| End-to-end encryption | Always on | Always on for messages |
| Owned by | Non-profit foundation | Meta |
| Data collected | Very minimal | More metadata |
| User base | Smaller | Billions |
Both encrypt messages. Signal collects far less data.
For analysts
In communication policies, I'd specify which apps are allowed for business decisions and how records are kept. Encryption and retention needs must be balanced deliberately.
History & origin
Moxie Marlinspike and Stuart Anderson founded Whisper Systems, releasing the encrypted apps TextSecure and RedPhone in 2010. Twitter acquired the company in 2011, after which the projects continued as Open Whisper Systems. The Signal app launched on iPhone in 2014 and merged the earlier Android apps in 2015. WhatsApp adopted the Signal Protocol for its billion-plus users in 2016. WhatsApp co-founder Brian Acton helped create the Signal Foundation in 2018 with $50 million US. Signal added usernames in 2024 and post-quantum protection in 2023. In March 2025, senior US officials accidentally added a journalist to a Signal group chat discussing military plans, an episode showing how human error can undermine strong encryption. In my view, Signal sets the standard other messaging apps are measured against.