This question was raised by one of my players who is playing a third version mystic from unearthed arcana (released on 13/03/2017).
To provide a couple of example scenarios:
- He has tried to use this on an animated armor (before it moved) to sense if there was a mind present.
- On a corpse to see if it was actually dead or just pretending to be.
He argues that according to the description of the telepathy feat, a telepathic connection is made between him and his target. And that he should be able to sense if there is a mind present to make this connection.
At 2nd level, your mind awakens to the ability to communicate via telepathy. You can telepathically speak to any creature you can see within 120 feet of you in this manner. You don’t need to share a language with the creature for it to understand your telepathic messages, but the creature must be able to understand at least one language or be telepathic itself.
This argument is seems backed by the description of the telepathy spell, which also mentions a telepathic link.
You create a telepathic link between yourself and a willing creature with which you are familiar. [...]
From a story/roleplaying perspective, this makes sense to me and I sort of agree.
Mechanically speaking it seems pretty overpowered for a second level feature. I know unearthed arcana isn't supposed to be perfectly balanced and imbalances are possible when using playtest content. But I'm more concerned with how to interpret the wording than with actual player power.
So far I've established that talking telepathically with a creature is like regular talking but instead of using sound waves you're using telepathic signals. And instead of targeting everyone within earshot, you're targeting one specific person. But I would be happy to change this if any literature was more specific.
I would prefer an answer with 5th literature sources but if these don't exist, I would be happy with an answer from previous editions as well.