Cosmic rays found in smartphones

[0] http://arxiv.org/abs/1410.2895

[1] https://www.google.co.uk/#q=1337647+sqm+to+sqft

(If they were sensitive enough the hardware would probably filter these out anyway.)

The application runs when the phone is not in active use. It launches itself when it detects a power source, and quits when the power is disconnected. No additional light shielding, such as tape, of the camera is required, other than placing the phone face-up (camera-down) on a table. In this way, no active participation is required once the application is installed and its operation should be fairly inobtrusive, which is critical to achieving wide participation in the smartphone community. To address user security concerns, no frames will be stored or up- loaded if the average pixel response value over the frame exceeds a threshold, such that full images cannot be re- constructed offline.

[snip]

Note that this assumes continuous operation; some degradation of observational power is expected, as phones will typically join the network during night-time charging. The observational power of such a network clearly hinges on the level of user adoption and continued participation.

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This makes sense, there's no need to operate during the day; in fact it's much better to operate at night when background light (and therefore noise) is likely to be lower. Cosmic rays don't sleep.