User blog comment:GreenMoriyama/Custom Item Concept - Silent Chime/@comment-22636720-20170201114315/@comment-3391671-20170202082234

This item purposely trades detection and a bit of &  for what some champions (primarily supports) would have as a starter item, such as  or : gold income. It hopefully causes them to choose between careful warding & passive income, or have this item to be more secure. But rest assured, this item doesn't completely rule out ganks by enemies, since they can take the opportunity to gank when this item is on CD (90 seconds). Plus, the detection is done every 6 seconds, not every second.

Some of your questions are answered in the blog, but here it is: " [...] to see ghostly footprints of any units, even if they are invisible or in the Fog of War." It may not be repeatedly mentioned, but it is intended to detect through Fog of War.

The CD is for the Active effect. Upon selecting the item as you may do for other items with active effects, the detection effect goes off and goes on cooldown immediately. It's not a cooldown for anything else. As described, the active does offer the detection even when in combat.

I felt that this item would work for midlaners because early game magic damage can be a horror to deal with, so having a bit more through this item could be a saving grace. I don't play competitive mid often, but I do not think this item is as irrelevant as is to.

All of the above pertains well for the starter item version of this item. I also provided a more mid-game version of it as a legendary item, something I might take when I've become a bit lazy with warding and want to know if there's a in bush. You also bring a good point that this would help champions such as and  dual each other better. And as you have picked up, it can also be a good counter-jungle item. It has its uses, my friend.