What exactly are you trying to capture? Your regex (.*\d{4}) doesn't match anything except the timestamp.
Based on your props config, I will assume you are looking for the Door name.
rex field=_raw "\d{4},(?<whatever_cam_is>[^,]*),(?<door_name>[^,]*),"
should give you whatever field the CAM refers to, and the door_name of "Outer Door".
Have you considered using a transform?
props.conf
[alerts]
REPORT-doorcontrol = doorcontrolcsv
transforms.conf
[doorcontrolcsv]
DELIM = ","
FIELDS = "timestamp", "whatever", "door_name", "alert_type", "alert_value"
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