When you initiate a conversation with someone on Signal, you and the recipient exchange so-called cryptographic keys. Only the person who receives your message holds the key to decrypt and read it. That means that if a government agency had a wiretapping order for your Signal messages, Open Whisper Systems would not have the key to decipher the messages and would be unable to comply.

Signal’s technology sets the standard for other messaging services, with its protocol being an open-source system that other companies can freely use. WhatsApp, Facebook’s Messenger and Google embedded Signal’s encrypted messaging system into their own apps this year.

Even so, security researchers said they preferred Signal over other messaging apps because it was more thorough in protecting users’ privacy. The only information Signal stores about users in its database is the last time someone connected to its server and when a person signed up for Signal. Other messaging apps maintain pieces of personal data on their servers.

By contrast, while WhatsApp enables Signal’s full encryption by default in messages, there are caveats. WhatsApp may retain some so-called meta data on conversations, including the phone numbers used in an exchange and the times that the messages were sent, according to the company’s privacy policy. WhatsApp also regularly accesses your phone number and contacts list, so the app can provide an up-to-date list of your contacts who use its service to make it easier to message them.

Google Allo, Google’s new messaging app that leverages artificial intelligence, does not enable Signal’s end-to-end encryption in all its messages by default. Google offers full encrypted messaging only in so-called Incognito sessions, a private mode that must be turned on manually. When you’re not chatting in Incognito mode, Google stores your Allo messages on its server.

Similarly, Facebook’s Messenger enables end-to-end encryption inside a private chat mode called Secret Conversations. But by default, normal Messenger chats lack that encryption.

Even though Signal doesn’t record your information, the app still works across devices, like a desktop computer and a mobile device. Messages and contacts’ data are stored directly on users’ devices and synchronized between them.