Android phone keeps starting clock/alarm app when I charge it up ........

[Gizmonster]

I've just recently acquired a Sony Xperia S (Android phone).
It's my 1st Android and touchphone, so I've been messing around trying to set things up.
I don't know exactly what I've done, or how I even mmanaged to do it, but everytime I plug the charger in and begin to charge the phone, the following message appears briefly on the screen, "App start, start of alarm and clock" and then the clock/alarm app starts up and prompts me to set the alarm.
Anyone any idea how to disable this please ??