AT&T Door Phone Controller Installation And Operation Manual page 82

A-2 DIP Switch Settings
Switch 6
Not used.
Switch 7
Not used.
Switch 8
Selects between Option Selection Mode and Normal Operation.
This switch acts as a Option Selection security switch. If this
switch is ON, any user can activate Option Selection Mode by
keying in "##3" on a touch-tone telephone set which connects
directly to the AT&T Door Phone Controller. When this switch is
OFF, Option Selection Mode cannot be activated. Normal
Mode = OFF; Option Selection Mode = ON.