Following a teardown of the iPhone 4S conducted by the iFixit team, among many intriguing features found, was a small black component that nobody seemed to know much about.
Located next to the ambient light sensor, the team realised they were looking at an intriguing new sensor. Every smartphone worth mentioning has its sensors that allow better gaming performance, help in orientation and have many other applications.
iPhones have their share of sensors, including infrared proximity sensors that switch off the sensitive touchscreen when the user is making a call so he or she won't inadvertently press any keys with their cheek.
Now, Siri has demanded the integration of another infrared LED sensor in the iPhone 4S; although the new sensor is always alert as long as the screen is activated, and is constantly searching for the user's face. This allows Siri to be ready for the user's commands as soon as the iPhone is raised to the face level.
This "raise to talk" feature instantly wakes Siri and requires the proximity sensor to emit infrared radiation at all times. For those concerned users, the iFixit reviewer pointed out that "Infrared light is non-ionizing, meaning it is a low-frequency radiation, lacking the energy to influence changes in DNA."