Whenever your iPhone 4S that is active is raised near to your ear,then there is a feature named “raise to speak” (which is already included in the iPhone 4S) – will activate Siri and you all are well aware that Siri is your personal digital assistant considered as the top best among the 10 great features of Apple iPhone 4S .
By making use of a proximity sensor, the raising action of the iPhone 4S will be sensed by itself with which the closeness of device to your face will be detected easily.These proximity sensors were included before on iPhone for the prevention of accidental input at time of phone calls.Where as the feature “raise to speak” Of Siri needs the iPhone 4S to be ready inorder to make the proximity sensors work on it.
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iPhone 4S’ Original teardown has been restored by the iFixit Teardown firm inorder to make the sensor involved get highlighted & it is also demonstrated how the IR light or the infrared light is emitted whenever the raise to speak feature of Siri is supported.
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Below given is the YouTube Video Showing how the proximity sensor of iPhone 4‘s gets activated when you are on a phone call,where as the iPhone 4S’ proximity sensor is activated anytime the display is put on.