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Siri knows when you're nearby

(CBS) - Siri is more aware of your proximity than you know.

The electronics repair site iFixit recently deconstructed the Apple iPhone 4S and discovered that an infrared proximity sensor was working overtime. Previous iPhone models have had a similar sensor, so why was it more active on this one in particular? Oh, Siri, of course!

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Infrared sensors have been used on previous iPhones to tell if you were talking on the phone, so it could dim the screen or hide the keyboard. Apple's latest model, however, has an always-ready personal assistant as its main draw. Siri uses the sensor to enable the raise-to-speak feature. Meaning, when you raise the phone to your mouth, it knows you want to talk to Siri.

Using an old webcam in order to see the infrared light, the iFixit team observed the sensor's habit of turning on whenever the iPhone's screen was active.

While infrared radiation might concern some, it's not clear if the iPhone is actually a threat because of mix conclusions over cell phone safety. We have fairy regular exposure to low frequency, non-ionizing radiation - microwaves and power lines, for example.

CNET: Cell phone radiation levels

We wouldn't suggest staring into the sensor all day, however. Those of you who are concerned can read a full report at CNET regarding cell phone radiation levels.

More than anything, the visual image of the iPhone 4S' infrared sensor light reminds of to make decisions over how much exposure to non-ionizing radiation we feel comfortable with.

There is also a creep factor of Siri watching and knowing our every move. Alas, our Siri obsession continues.

Chenda Ngak

Chenda Ngak is the science and technology editor at

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