Metro alarm

The ideea of metro alarm is to notify the user about his metro station, when he is sleeping or hardly thinkink. Actually this is a phone based application, that countes stations. The main problem here is: how can we count station? How does the phone know when you arrive to the station. Well there are a few posibilities that have been explored by the people.
   -  You can do voice recognition, so the phone can listen using the microphone and to process the voice captured. I see here 2 problems. First one is that you have to make some powerful calculations, that will consume your battery. Second is the background noise.
    -  My ideea (i am sure not only mine), is to use accelerometer. So when the train accelerates/decelerates you will see some changes on one of the axis. The problem here is that the phone have to be in the same position, or you can make adaptive algoritm, to automatically adjust the settings when you move the phone, but i think it is to complicated.