An encrypted instant messaging system from the Signal Technology Foundation. Introduced in 2014, Signal uses telephone numbers and cellular service similar to text messaging. It also supports voice and video calls, as well as sending voice notes, images and videos to another party.
Although phone numbers are the primary contact mechanism, Signal also supports usernames for people who want their numbers kept private. Signal supported standard SMS messaging for Android phones, but that was dropped in 2023.
A Signal Faux Pas
In March 2025, a Signal group chat was used by U.S. officials to discuss the planned bombing of Yemen to stop the Houthis from sinking commercial ships in the Red Sea. The chat, which included the secretary of defense and vice president, had inadvertently invited the editor-in-chief of The Atlantic magazine to participate.
According to NPR, the Pentagon had warned employees only days before to not use Signal for classified information because of Russian hacking. Nevertheless, Signal is considered one of the most secure messaging apps on the market, and the Yemen incident would never have caused a stir if a journalist had not been accidentally invited. See
text messaging vs. instant messaging and
SMS.