Phones

Camera phones and near infrared

Older camera phones didn't have enough pixels for the chromatic aberration of infrared light combined with visible light to be significant. But now that the aberration spreads across multiple pixels of high-resolution sensors, cameras require an infrared filter. You can point low-resolution camera at the emitter of a remote control, most of which use infrared light, to see the pattern of light being emitted. A high-resolution camera will not sense the light.

Sonim XP phones

I was annoyed at how whenever I accidentally pressed the yellow side button, the TDC app would start. I learned from a discussion at T-Mobile support site, https://www.t-mobile.com/community/discussions/devices-orders/sonim-xp3plus-issues-apps-how-to-stop-direct-connect-asking-me-to-activate/132775 , that I could assign the yellow button to any app, so I assigned it to Calculator, and now it opens Calculator if phone is open and does nothing if phone is closed.

Options > System settings > System > Programmable Keys > Select PTT Key app