Insight Whether Someone is Alive is Not According to What You See

Rabbeinu Yitzchak, the son of the Ra’avad, was a great Kabbalist, to whom Eliyahu the Prophet was revealed. Rabbeinu Yitzchak was blind. But he could distinguish between alive or dead by sensing in the air.

(See talk of the Lubavitcher Rebbe King Moshiach Shlita, Eikev 5751 (1991))