It is very easy to fool humans.
If there where any mechanical artifacts out there of no human origen, then these artifacts will be pretty safe from being uncovered just by placing something that may look like a tether below them.
It will not matter what the top part will do: glow, change shape, release other objects/drones, etc. By that simple "trick" they will be forever safe from being uncovered by human observers.
Even if some human observers discover them, the camouflage still will be effective because these humans that had uncovered them will be dismissed by almost all other humans, for almost all humans these artifacts, by the mere trick of attaching something similar to a tether below them, will be balloons.
It will not be difficult for such artifacts to discover how easy is to fool humans.
Are there any "crazy" reports of UFOs that looks like balloons? It will not matter if these reports exist we "know" that such reports can be dismissed out of hand, we are too "clever" to be fooled by "balloons".
"It's easier to fool people than to convince them that they have been fooled.” ― Mark Twain.
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