Blindsight?

[Sindeloke]

In previous editions blindsight was quite powerful - you essentially auto-detected anything. The SRD even specifically calls out that you don't need to make Spot or Listen checks to notice things within your blindsight radius, and says that things like blur and invisibility are useless against you.

Like everything else in 5, though, blindsight seems quite vague this time around. It just says you can see with senses other than sight. It doesn't even mention illusion spells, much less skills like Stealth or Perception. So... auto-detect or not? Does a dire bat need to make a check to find you if you're hiding from it?

My inclination is to say that no, Stealth works just fine against blindsight. Owls, for example, can hear mice move underground from more than 60 feet away, but they have to stop and listen to do it. A bat can echolocate through a dense forest, but if it's busy chasing moths it probably doesn't notice the difference between "solid obstacle shaped like a fencepost" and "solid obstacle shaped like a branch" any more than a human notices the difference between two trees on the side of the highway. A dog can smell that there's food nearby but he still has to sniff around a while to find the dumpster.

That said, the specific radius thing and the general legacy of prior editions suggests it ought to be auto-detect still.

[Louro]

BLINDSENSE
Starting at 14th level, if you are able to hear, you are
aware of the location of any hidden or invisible creature
within 10 feet of you.
I would say you need something to hear. A creature wich is levitating will be "inmune" to your blindsight. It's just a 10 feet radius, so you can assume the if a creature is moving (or attacking) within that radius, and there is not an orchestra playing in the room, you can pinpoint that creature.

[Regulas]

I would say you need something to hear. A creature wich is levitating will be "inmune" to your blindsight. It's just a 10 feet radius, so you can assume the if a creature is moving (or attacking) within that radius, and there is not an orchestra playing in the room, you can pinpoint that creature.

This simply means that you need to not be deafened/too loud ambient noise and does not imply that they have to explicitly be making noise to be detected.

[Sindeloke]

That's rogue blindsense, anyway, which is distinct from the vaguely-defined blindsight of the Monster Manual and page 183 of the PHB. Although I'd forgotten about that, that's a good point - blindsense was always inferior to blindsight in previous editions, and if blindsense is auto-detect surely blindsight must be.

[Giant2005]

Stealth obviously does work fine against Blindsight, otherwise it would have been pointless giving a passive perception to all of those critters with Blindsight in the MM.

[Yagyujubei]

In previous editions blindsight was quite powerful - you essentially auto-detected anything. The SRD even specifically calls out that you don't need to make Spot or Listen checks to notice things within your blindsight radius, and says that things like blur and invisibility are useless against you.

Like everything else in 5, though, blindsight seems quite vague this time around. It just says you can see with senses other than sight. It doesn't even mention illusion spells, much less skills like Stealth or Perception. So... auto-detect or not? Does a dire bat need to make a check to find you if you're hiding from it?

My inclination is to say that no, Stealth works just fine against blindsight. Owls, for example, can hear mice move underground from more than 60 feet away, but they have to stop and listen to do it. A bat can echolocate through a dense forest, but if it's busy chasing moths it probably doesn't notice the difference between "solid obstacle shaped like a fencepost" and "solid obstacle shaped like a branch" any more than a human notices the difference between two trees on the side of the highway. A dog can smell that there's food nearby but he still has to sniff around a while to find the dumpster.

That said, the specific radius thing and the general legacy of prior editions suggests it ought to be auto-detect still.

I'd say that you can hide from someone/thing with blindsight if you passed a check to remain perfectly still, but the second you make a movement inside the active radius you're auto-detected. This would apply to illusion spells as well imho, blindsight would negate things like blur and invisibility, but mirror image would be effective at distracting it.

I always thought of blind sight as the ability to sense motion without the need for sight or hearing.