Can anyone explain what the cabin chimes mean on a UAL flight?

I fly this airline frequently and seem to THINK I know, but would like to hear it from someone in the know.

After take-off, there are 2 chimes. I assume this signals to the flight attendants it is safe to get up, etc.

Sometimes during a flight you hear a high-low chime, and sometimes 2 high-low chimes. Is this simply paging the other flight attendants?

Thanks