Default Friend's S3 started randomly making beeping noises and showed a weird image...

My friend's S3 was plugged into the wall outlet, and it randomly started beeping (as if you were plugging it in). When she hit the home button, she would then see the following image:




Does anyone know what this image represents? I also own an S3 but have never seen anything similar. The screen above was not her home screen either.

Thanks!