Over the last few years, Signal has become one of the most popular messaging apps. Favored by tech giants, cybersecurity experts, journalists, government officials, and many more, Signal has gone from a darling secret of the security community to a group chatting phenomenon.
It’s recently been thrust into the spotlight after the editor in chief of The Atlantic, Jeffrey Goldberg, was inadvertently added to a Signal group chat where top Trump administration officials discussed bombing Yemen.
According to Goldberg, Vice President JD Vance, Defense Secretary Pete Hegseth, Director of National Intelligence Tulsi Gabbard, and Secretary of State Marco Rubio all appeared to be members of the group chat, which was called “Houthi PC small group,” referring to the principals committee.
Signal founder and former CEO Matthew Rosenfeld, who goes by the pseudonym Moxie Marlinspike, poked fun at the botched chat in a post on X, formerly Twitter, on Monday.
“There are so many great reasons to be on Signal,” he wrote. “Now including the opportunity for the vice president of the United States of America to randomly add you to a group chat for coordination of sensitive military operations.”
Elon Musk has also endorsed Signal before, writing simply in a post on X in 2021, “Use Signal.”
He changed his mind about the app a few years later, though, writing in May 2024 that it had “known vulnerabilities.” Signal’s president, Meredith Whittaker, later told Wired she went two nights without sleeping “just dealing with Twitter stuff.”
“He’s been a fan. So I don’t know what changed,” she said. “What I do know is that, as far as we know, the claim was completely baseless.” Whittaker added there was no “serious report” backing up Musk’s claims.
Signal is owned by the nonprofit Signal Foundation, which was set up in 2018 by the app’s cofounders, Rosenfeld and Brian Acton, who also cofounded WhatsApp. The foundation has five board members and serves to “support Signal’s growth and ongoing operations as well as investigate the future of private communication,” according to its website.
Here’s a guide to the Signal app, including why it’s become so popular.
The Signal app, explained
Signal is safer and more secure than most messengers because of a process called “end-to-end encryption.” This works by encoding a sender’s message in such a way that only the intended receiver can view it.
Neither Signal, nor your phone company, nor the government can read your messages. That’s why it has remained popular.
However, Signal’s messages are only secure if both the sender and receiver are using the app.
If you prefer to communicate through Signal, the app has a simple feature to invite someone to download it. It’s also just as easy to block someone on Signal from contacting you.
Encryption itself isn’t a unique feature, as apps like iMessage, Telegram, and WeChat also offer it. But one of Signal’s selling points is that its source code is also publicly available, so experts have been able to poke and prod at its defenses for years, strengthening it in the process.
Signal’s key features
Signal is similar to other messaging apps but with more robust security features. It’s available for free on iPhone, Android, Mac, and PC.
Android users can even set their default messaging app to Signal if they want to.
On a basic level, you can have one-on-one conversations with someone or start a group chat on Signal. In these chats, you can send pictures, videos, internet links, voice messages, and more.
Signal’s beta version has tested new kinds of chats with forum-like features, including group admins, updates, and timers for disappearing messages. For now, groups are capped at 1,000 people, but adding and removing people from a Signal group is simple.
If you’re concerned about someone accessing the app from your phone, you can lock the Signal app with the same passcode or fingerprint scan normally used to lock your phone.
Signal requires a phone number to join the app. To keep yours private, you can sign up with a Google Voice number. Apple users will want to visit their privacy settings within the app and turn off “Show Calls in Recents” to prevent their history from syncing with the cloud.
You can also set your messages to disappear over time, or set photos to disappear after a single viewing.
Barbara Smith and Vivian McCall contributed to an earlier version of this story.
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