  The total area of silicon in cell phone camera sensors worldwide surpasses
that in any experiment to date. Based on semiconductor technology similar to
that found in modern astronomical telescopes and particle detectors, these
sensors can detect ionizing radiation in addition to photons. The Distributed
Electronic Cosmic-ray Observatory (DECO) uses the global network of active cell
phones in order to detect cosmic rays and other energetic particles such as
those produced by radioactive decays. DECO consists of an Android application,
database, and public data browser available to citizen scientists around the
world (https://wipac.wisc.edu/deco). Candidate cosmic-ray events have been
detected on all seven continents and can be categorized by the morphology of
their corresponding images. We present the DECO project, a novel particle
detector with wide applications in public outreach and education.
