Here’s why you can’t have Siri on iPhones prior to iPhone 4S [UPDATED with clarification from iFixit]

UPDATE [Wednesday, November 9, 2011 at 3:31pm ET]
A comment from iFixit added to the article bottom clarifies that Siri functionality regarding the iPhone 4S’s proximity sensor is likely software-based rather than stemming from hardware changes, as implied in the headline.

Ongoing efforts to port Siri to other iOS devices (here and here) have given hope to enthusiasts eager to port the iPhone 4S-exclusive digital assistant to prior iPhone models. But while the Siri port may eventually prove feasible, the full experience will not be possible on any other iOS device apart from the new iPhone 4S. iFixit discovered today that iPhone 4S features a tweaked proximity sensor, basically an infrared LED light which can tell when the user brings up the device to their face in order to turn the screen and touch interface off. But what’s so special about the proximity sensor in iPhone 4S compared to other iPhones?

The iPhone 4S  has a neurotic tendency of always wondering how close your face is. As long as the screen is activated, that IR sensor will be shining brightly. Siri is ready and waiting to answer her master’s beck and call at any time. 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.

In other words, proximity sensor on prior iPhone models would only switch on when a call was initiated, not whenever the screen was activated. This iPhone 4S-specific tweak makes a big difference in user-friendly Siri implementation on the device. Summing up, while Siri may eventually be hacked to work on iPhones prior to the iPhone 4S, you won’t get the whole experience, which is typical of Apple.

UPDATE: Some people are not buying this as is. Truth be told, the original iFixit article is a bit inconclusive, leading some people to paint our ‘Siri on older iPhones may not provide the full experience based on the assumed proximity sensor tweak’ argument as bogus. We’ve reached out to iFixit and here’s their official clarification:

The IR LED definitely appears to be different on the 4S when compared to the iPhone 4, but we don’t think that the hardware change is causing the light to be continuously lit. That functionality is built into the software system, since it’s the software that tells the light when to turn on, and when to turn off.

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