First I recognize you said maybe, but the range would need to be much larger than 100 meters.
As out of the box hobbyist drones can already travel at 50 mph [1] (or more I assume). And 100 meters assuming approach of a stationary object would provide just over 4 seconds for the drone to respond and avoid the object.
While 4 seconds is sufficient time, it will lead to drones flying very close to objects before avoiding them which will not inspire public confidence. Also as faster drones appear that window will become even smaller. They should probably have radar with a range measured in nautical miles to avoid having to implement a new system almost immediately. I would say at least 5 nautical miles, although I feel even that would be on the short sighted end of implementation.