Shinobi develop their senses to an extreme level, attmepting to take in every detail. This coupled with a natural sensitivity to chakra, you're actually able to feel the minute amount of chakra everyone releases constantly.

You automatically gain an awareness check against anyone that comes within your SPR in yards. The opponent's stealth and disguise doesn't matter for this, you must merely score higher then the person's Level+10 on your awareness check. If you are successful you know someone is there, their general distance and direction. You can also tell the difference between a normal person, a ninja, and if it's 'something else' with a wildly different amount of chakra or chakra signature (such as a demon).
If you beat the check by 10 you can also tell the difference between chakra signatures of individual people. This does not tell you the person's exact location, only general direction and distance. They still have total concealment from you unless you can see them through some other means.
Favored Attributes
Spirit, Mind