The teardown experts at iFixit revealed on Wednesday that the proximity sensor in the iPhone 4S has a newly modified infrared component that's enabled whenever the handset's LCD screen is active. Previous iPhones only enabled the proximity sensor when users were on a phone call or utilizing an application that required users to hold the device up to their ear.
Now, with the iPhone 4S, the infrared sensor is always working while the handset is in use, allowing users to utilize the raise-to-speak feature available with Siri voice recognition. The sensor allows the touchscreen on the iPhone 4S to automatically turn off so that actions cannot be taken by pressing the screen when either Siri is being used or a phone call is being made.
"Siri is ready and waiting to answer her master's beck and call at any time," the solutions provider said. "And in order to be as attentive as a personal assistant ought to be, Apple had to design the proximity sensor to be as vigilant as Big Brother, but as cute as LIttle Sister.
"So whenever the screen is active, the proximity sensor is active too. Thus, whenever you raise the iPhone 4S to your face, Siri is ready to take orders."
The site also noted that the constant output of infrared radiation isn't a "big deal," as infrared light is non-ionizing and emits a low-frequency radiation.
iFixit first took a look inside the new iPHone 4S last month, though the new proximity sensor was not given much notice. The initial take made mention of a slightly larger batter and new baseband chip found in Apple's fifth-generation handset.
Users can invoke Siri on the iPhone 4S by holding down the handset's home button, or raising it to their ear and speaking directly into the microphone. The raise-to-speak function can be turned on or off in the device's settings.
Siri is perhaps the most significant new feature in the iPhone 4S, and remains exclusive to Apple's latest iPhone model. The inclusion of a new proximity sensor could also provide some explanation as to why Apple has said it has no plans to bring Siri to other devices such as the previous-generation iPhone 4, or even the iPad 2, which is powered by the same A5 processor as the iPhone 4S.