Smartphones are making the war in Ukraine the most intensively documented in history, changing the shape of the conflict and transforming the world’s understanding of it. Each of the millions of devices in and around Ukraine are sensors that can provide data located to place and time. Their microphones and cameras can record and transmit sounds and images that depict the facts of war or provide tools for propaganda. These records are allowing investigators to build extensive visual archives of the conflict that could eventually provide a reckoning for war crimes.