RestInPeace is an application that sounds an alarm when the phone registers itself with a pre-defined GSM/WCDMA CellID.

Useful when travelling on a train or bus - set it to ring an alarm when the phone logs in to a cellID located at the destination of your trip and you can safely fall asleep.

An alarm based on location rather than time is better because it'll always alert you in the correct time, even if the train arrives earlier or late.