Your ki, your life energy. I and others of my family line can feel what we call the Veins of the Dragon, which holds the souls of all living things. My own sense of it does not extend as far as you said that device can, but I have always been precise.

[There's a bit of pride in that statement--Fu had certainly had a farther range that she, but she had always had a knack for pinpointing those out of her sight.]