iFixit finds the "multi-purpose component that connects the earpiece speaker, IR blaster, and a sensor array hosting the ambient light sensor and a second IR sensor." Click here for larger image. (Source: iFixit)
Thanks for the "QNH" aviation explanation. Certainly the same approach could work for SmartPhones: the GPS would provide a location and the nearest reference barometer could provide the correction factor. The one remaining issue would be the pressure differential inside the building. Many buildings run at positive pressure which would cause the "altimeter" to read a lower floor level than it should (denser air). Perhaps a simpler approach would be for the GPS to detect entry into the building perimeter, use the indoor ground level air pressure as the barometric pressure reference. It could then compute floor levels by the associated pressure reductions as the air pressure reduced with increasing altitude.
Thanks. Yes I was disappointed when I found out an altimeter is really just a barometer with more math. (In other words, you subtract the local weather conditions.) Once I wanted a fancy watch with an altimeter on it for hiking but when I found out the altimeter was just a barometer, I decided it was just a toy (for my purposes). An altimeter wasn't going to keep me from getting lost.
The same problem applies to aircraft altimeters - the pilot gets a "QNH" (I think) figure which is the sea level pressure at his location, puts it in and the altimeter is accurate. So all you need is some way of (preferably automatically) telling the phone the QNH and it should be accurate...
The sensor claims to be able to read your barometric pressure altitude within 3 feet (which would define the floor of a building). The challenge is that is needs to adjust for weather related pressure changes which could cause the readings to be off by 30 floors...
Sounds like we need remote bluetooth temperature sensors for the iPhone - we care about the temperature outdoors as we drive, not in our pocket where the phone is resting. Maybe some of our car sensors can grant read-only access to our SmartPhones.
@DrQuine: "It also provides an interesting object lesson in atmospheric pressure in SI units." Interesting! Thanks Dr. Quine. So what you're saying is the Bosch MEMS sensor can measure such small pressure changes that it can tell if you're on the 4th floor or the 30th floor and not be affected by general pressure changes in or outside building (weather, HVAC)?