How does the compass application on a iphone work?

It shows the compass directions N, S, E, and W on the display and the image
rotates as you turn the cell phone so N always points north.

It can't be accelerometers. They are only accurate for a short time and need to
be constantly re-referenced to north. So how would it know the initial orientation
of the phone relative to north?

It can't be GPS because that only crudely gives location information and not
phone orientation.

It can't be multiple cell tower triangulation because that would require multiple
iphone antennas and picosecond speed electronics which if much too complicated.

There's only one way I can think of, and that is if either a real compass is inside
the iphone that provides the north reference, or some other way to detect the
direction of the earth's constant magnitude magnetic field.

IMagic

Most Smart phones have a built in GPS, combine that with google maps? You would be surprised. In AU our emergency number is 000 for landlines on mobiles it is 112, not many know this so it can triangulate a position of a mobile phone, because we see a lot of US movies 911 and 111 ( NZ) have to be switched through our network as well. In AU even if you don't have a signal from you own carrier you can get an emergency call in on any carrier in range. As for a compass being inside all the electronics would interfere? Locations are only and estimation anyway. My iPad is at home but location finer shows it 100M away in the next street? GPS give you direction North. South etc.

The component is called a three-axis magnetometer. Basically (as I understand it) an electronic compass that measures its location in the X, Y and Z axis relative to the earths magnetic field.

See link.

Actually its something like that. It senses orientation relative to the Earth's magnetic field using the Hall effect:
http://en.wikipedia.org/.../wiki/Hal…

Actually it is GPS bro steve(RIP) talked about it in one of his lectures + they can't put a real compass inside the iPhone because they were complaining about space and stuff ( Apple: the hardest part was to get all the pieces insides the iPhone it self… ) and to prove that there's no real compass inside just try to approach a magnet to the iPhone while the compass application is open and nothing will happen, a real compass would turn to face the magnet