Blindsight and Tremorsight and Hiding

[Yakk]

I'm thinking of stating that, outside of unusual situations, everything is "lightly obscured" to someone using Blindsight or Tremorsense.

That would mean that seeing things with their actual eyes in bright light has some utility for those creatures.

For Tremorsense, particularly well conducting surfaces (solid rock in some cases, but for a desert creature it might be sand) would remove that obscurement. And moving at full speed would "light you up" regardless.

Then, as a more general Stealth rule, you cannot start Hiding while lightly obscured, but you can remain Hidden while lightly obscured.

This means that Dragons (for example) don't auto-detect hiding people within 60; you just can't start hiding within 60 feet of them.

[OldTrees1]

I usually take a different tack:
Beings with unusual senses are competent with those senses. Beings proficient with stealth are competent with hiding from various senses. I am not proficient with stealth or have unusual senses, so I will assume favorably to both when in doubt. In general, for these exotic senses, there is enough concealment to hide but not enough to penalize perception.


Some blind alien species out there has an RPG that includes a "Deaf hearing" feature for hearing without using your ears. They don't fully understand how that sense works, but they assume there must be ways to hide from it. They might even make a distinction between "Deaf sense" with limited perception and "Deaf hearing" where the sense is as strong as hearing. If it is not already obvious our vision would be an example of "Deaf hearing".

[Yora]

I've been pondering the same thing a few weeks back, and came to the conclusion that blindsight really looks like it's supposed to work like "vision", but regardless of eyes or light.
Light levels are irrelevant, and as blindsight is concerned, everything behaves as if "well lit". But to evade being seen by blindsight, you can still use all other kinds of concealment that are not based on light levels. Blindsight shouldn't let you see through a curtain, for example. Or even though dense fog or smoke. Blindsight only ignores dim light and darkness, is what I was taking away.

Tremmorsight is a wholly different story, though.

[Chronos]

When this came up at my table, we came to an agreement that you could hide from any sort of sense, but that a creature trying to hide from a sense they don't have would be at disadvantage on their Stealth roll, because you're not as familiar with what sort of telltales to avoid.

[Guy Lombard-O]

I've been pondering the same thing a few weeks back, and came to the conclusion that blindsight really looks like it's supposed to work like "vision", but regardless of eyes or light.
Light levels are irrelevant, and as blindsight is concerned, everything behaves as if "well lit". But to evade being seen by blindsight, you can still use all other kinds of concealment that are not based on light levels. Blindsight shouldn't let you see through a curtain, for example. Or even though dense fog or smoke. Blindsight only ignores dim light and darkness, is what I was taking away.

So does that mean that if you're hit with the Blindness(/Deafness) Spell that your Blindsight would also be disabled? If wondered if that's how that interaction is supposed to work.

[Kane0]

For Tremorsense, particularly well conducting surfaces (solid rock in some cases, but for a desert creature it might be sand) would remove that obscurement. And moving at full speed would "light you up" regardless.


Walking without rhythm costs half your movement but gives you light obscurement against tremorsense.

[Spiritchaser]

Walking without rhythm costs half your movement

Unless you select the fremen background.

[Yora]

So does that mean that if you're hit with the Blindness(/Deafness) Spell that your Blindsight would also be disabled? If wondered if that's how that interaction is supposed to work.

Good question. The name implies that it wouldn't. But only a few creatures are mentioned to not gain their blindsight from their eyes. Bats and grimlocks obviously wouldn't lose their blindsight from a blindness effect. But with dragons it doesn't say if it relies on their eyes or where the ability comes from at all.

--

Looking a bit deeper into it:

Oozes all have blindsight 60 ft. and are blind beyond this radius, and they all have condition immunity to blinded an deafened. They don't have any sensory organs. They just have blindsight with no explanation.

Grimlocks have blindsight 30 ft., or blindsight 10 ft. if they are deafened. They can't use their blindsight at all when they are both deaf and can't smell. Since they don't have any eyes, they have immunity to being blinded.

Bats have blindsight 60 ft., which they can't use while deafened. They are not immune to being blinded, since they still have normal vision when there's light.

In all these cases, it's quite clear that blindsight works completely independent of eyes.

(Devils all have Devil's Sight, which explicitly states that their darkvision works in magical darkness. This is a completely different ability.)

One important detail I found is that the blur and mirror image spells specifically say that the effect of these illusion spells do not work on creatures with blindsight.
There is however no such note on hallucinatory terrain or minor image.