With the Gigaset S1 handset you can program time control in the menu item "Sound Settings" - "Ringer Settings".
These settings allow you to define a period of time in which the handset does not ring at all, or in which it rings in a different volume.
If the ringer volume has been set off within the defined period of time, the handset shows the "Ringer - Off" symbol in the standby mode.