Edward Snowden, who blew the whistle on NSA surveillance of U.S. citizens, knows a thing or two about spying. He’s now released an app, Haven, that makes it easier to defend yourself against the most aggressive kinds. Haven, now in public beta, turns any Android smartphone into a sensitive security system. It’s primarily intended to be installed on a secondary phone — say, last year’s model — which then takes photos and records sound of any activity in a room where it’s placed. Haven will then send alerts of any intrusion to a user’s primary phone over encrypted channels. Get Data Sheet, Fortune’s technology newsletter. The announcement for the app says it’s designed “for investigative journalists, human rights defenders,” and others who might be targeted by powerful enemies. According to The Verge, Snowden was encouraged to develop the app by a lawyer who fought to bring down Chadian dictator Hissene Habre. One commonly cited use case for Haven is protecting laptops holding sensitive information, which can be relatively easily compromised if someone gains physical access. Snowden, who lives in Russia because he faces espionage charges in the United States, has adopted extensive personal security measures himself, and reportedly doesn’t even carry a smartphone anymore.