A couple of years ago, I found an app for my phone that "simulated" a Heads Up Display (HUD). It showed all the neat stuff you would see in a real HUD- altitude tape, heading, speed tape and attitude. Cool! Or so I thought. Just for jollies, I tried it during a soaring flight. It turned out that the data provided from the phone's accelerometers assumed you were sitting on the ground, with a gravity vector directed downward. In the air, a coordinated turn tilted the attitude line to the apparent gravity vector, i.e. 45 degrees off while in a 45 degree bank.

A real AHRS uses more sophisticated sensors to give an accurate horizon. I doubt there are phone apps that can do the same. I could be wrong, but from what I've seen so far, AHRS phone apps are amusing toys, and nothing I would rely on in flight. If you know of an app that is better, let us know. Not that I would use it in IMC flight, but cool apps are, well....COOL!