filterAlarm alarmEvent.get('source') doesn't work

Ultimately I would like to filter out certain alarms that contain a certain string within their source, but I can’t seem to target the source component of the alarm and I don’t know why.

source = alarmEvent.get('source')

returns no warning boxes. However:

source = alarmEvent.get('name')

will return warning boxes every second. Why can’t I target the source of the alarm?