The Sensing Technique, used by sensor typeshinobi, allows users to detect chakra. Using this technique, sensors can easily detect, and track down targets. The range of this technique varies between sensors.
Unique Sensory Techniques
Spider Web Area - Exclusive to Kidōmaru. With this technique, he is able to send chakra through the web to detect the approach of any enemy, that touches the threads. The web is so sensitive, that not even the slightest disturbance of the air goes unnoticed.
Mind's Eye of the Kagura - Exclusive to Karin. With this technique, she is capable of finding, sensing and tracking any individual over vast range by focusing and opening her mind's eye.
Rain Tiger at Will Technique - Exclusive to Nagato. Using this, he is capable of creating falling raindrops, which are closely linked to his senses. When the rain is obstructed by a chakra belonging to someone not of the village, the existence of the intruder can be detected.
Sensing Water Sphere - A sphere made out of Water Release that lets the user monitor the surrounding area. Despite the usefulness, the sphere itself does not provide a great form of detection, unless it is teamed-up with a barrier.
Throughout the series, various characters have commented on the feel of chakra and similar comments regarding the ability to sense high, foul or potent levels of chakra a little, leading to the possibility that chakra sensing is merely a more refined version of this by either teaching or being simply born more "sensitive".