The CRAYFIS project is a novel approach to observing cosmic ray particles at the highest energies.It uses the world-wide array of existing smartphones instead of building an expensive dedicated detector.

Modern smartphones contain high-resolution cameras with digital sensors which are sensitive to the particles in a cosmic ray shower. They know where they are (GPS) and can upload their data (wi-fi). Most importantly, there are 1.5 billion active smartphones spread across the planet. Essentially, this detector has already been deployed; all that is missing is the app to collect the data

The CRAYFIS app operates in a manner similar to a screensaver. When the phone is connected to a power source and the screen goes to sleep, the app begins data-taking. No active participation is required on the part of the user after the initial download and installation.

Source: Crayfis: The app that turns your phone into a cosmic ray detector.

Wonder how much battery it eats?