Blindsight/Tremorsense vs. Invisibility

[BlacklightVirus]

Okay, here's a quick question for y'all since it might be coming up in my campaign in the near future:

The rules say that an invisible creature can't be seen without either magic or "a special sense", which I take to mean truesight. But what about other non-visual senses? Like say if the party's Druid wild-shapes into a bat and uses its echolocation? Or if they have a pet with tremorsense and the invisible person/thing is moving along the ground? Or (homebrew incoming) they have access to the fantasy equivalent of a thermal camera and the invisible person/thing gives off heat?

Would any of those senses manage to overcome the invisibility? Or is the party out of luck without something like See Invisibility or True Seeing? Or is it just up to DM decision at that point?

[JackPhoenix]

Bat echolocation is blindsight, and works fine. Tremorsense tells you the invisible creature's position, but doesn't allow you to see it. As for the thermal camera, depends on how it's worded.

[strangebloke]

blindsight is not sight (and is thus not disabled by obscurement or blindness) but per sage advice it functions as sight for purposes of seeing anything within the radius. If this was unclear from RAW, its certainly clear by RAI: https://twitter.com/JeremyECrawford/status/972239019642781697?s=19

tremorsense just lets you pinpoint location within its radius. You still make attacks against invisible/unseen creatures with disadvantage, and they still have advantage against you, but you don't have to guess/make a search check to be aware of an unseen person's location. (and I'll argue this pretty clearly proves that you don't just automatically know the location of an invisible, unhidden creature by RAI - why would this feature exist if that were the case?)

Blindsense is trmorsense with a different condition.

[Greywander]

Blindsight allows you to see invisible creatures. By janky RAW, being able to see an invisible creature isn't by itself sufficient to remove disadvantage from your attacks, but most DMs will rightly decide that that's stupid.

IIRC, it's unclear if tremorsense is meant to act as a form of sight. It doesn't say that it does, so RAW even with tremorsense it only tells you where the invisible creature is. The D&Done playtest makes this explicit: tremorsense is not a form of sight. Personally, I think that's dumb, and defeats the point of even having tremorsense. Tremorsense, in my mind, is like Toph's ability from Avatar: The Last Airbender, and functions well enough to work as an alternative to vision.

I think truesight explicitly allows one to see invisible things, though I'm too lazy to look it up to confirm.

For the thermal camera, that's a DM call. Personally, I'd say no, as IR light is still light.

[Angelalex242]

Thermal camera is janky, I think. It can reveal sources of heat that are average human temperature (or elf temperature, etc), but the thing about thermal cameras is, it'd be difficult to determine friend from foe.

[da newt]

By strict RAW blindsight does NOT allow you to "SEE" anything (MM pg 8-9 has tremorsense too and also PHB pg 183-4), but as posted above JC has tweeted that even though it does NOT say you can SEE, you should treat it as if it did, and Tasha's Blind Fighting FS does add that in addition to blindsight 'you can effectively see anything that isn't behind total cover' and 'you can see invisible creatures unless they hide from you'.

The strict wording of unseen attacker and targets (PHB pg 194-5) makes a mess of things because it very specifically requires that the target / attacker can be "SEEN".

By strict RAW a purple worm cannot see so every attack it makes is at DISADV and every attack against it is with ADV.

I don't know if anyone actually follows the strict RAW as it is an illogical mess.

[BlacklightVirus]

Thank you all for your responses! I was a bit confused by the whole thing, so I'm glad I got some outside readings.

Regarding the thermal camera (in the form of a circlet, but whatever), the primary wording is that it makes warm objects appear to glow for the user within a certain range. I'm inclined to agree with Greywander's ruling on it not being able to circumvent invisibility, if only to keep it from being OP (the party that'll be receiving it is currently Level 5).

[OldTrees1]

I would rule:
Blindsight and Tremorsense ignore Invisibility but don't ignore Stealth.

Invisibility would block Thermal Vision to some degree. Invisible people still leave footprints so they would still lead some heat traces on the air/surfaces.

Your thermal camera makes "warm objects appear to glow", and then the user uses normal vision to see the light. Consider how do you rule someone under the effects of Light and Invisibility? I would say Invisibility suppresses the light.