What is the difference between a dSF11, dSF12 and dSF20? digitalSTROM Support September 28, 2018 06:02 Updated Follow The filter has been constantly optimized (better filter performance, function display etc.). The dSF20 should be used for new installations. Related articles Which smoke detectors can I use with digitalSTROM? How many filters dSF need to be installed? Why is a digitalSTROM meter (dSM) required?