Here are some starter guides ...
Regarding your app, here are some questions for you ...
- Does the Arduino have persistent storage to hold its schedule of alarms?
- Which flavor of BlueTooth do you plan on using? BLE or pre-BLE?
- What types of alarms?
- klaxon (on/off?)
- variable text display?
- choice of LED on/off?
- What type of schedule(s)?
- repeating daily?
- repeating weekly?
- one time?