If you have a Door station and Ringer to ring the house phones, but do not have a telephone Line Connected, so the Door Station is for Internal use only, please read the following instructions..
Since the telephone line is not connected you will get a Phone Trouble Alarm. You can check Configuration > Modules & Settings > Ignore Line Cut which will prevent the Phone Trouble alarm, but this setting will cause the local phone offhook not to be detected so you would not be able to talk to the door station, and the ringer may keep on ringing.
Uncheck "Ignore Line Cut"
Go to Security Types Settings > Non-Detector alarms and see 4 - Phone Trouble. By default this is assigned to Line Cut Alarm Type
Change this to Null Alarm
This will prevent the Phone Trouble alarm from occuring and will allow the Door station ringer and local phone to work