Re: Rinnegan allows the user to be a sensor!
More than saying it as "Sensing", I would say that they can see chakra with the Rinnegan eyes.
Otherwise, the six paths of Pain could have sensed Kyuubi's chakra inside the Village instead of asking for Naruto.
The Pain fighting with Kakashi could have sensed the difference between Kakashi's lightning clone and the original.
When Karin used the sensing ability to find out Danzo, Fuu found out that they are being tracked.
But when SM Naruto tracked Nagato throough chakra, Nagato was shocked.
Madara and Obito got Mokuton as well as Sharingan to sense the chakra.
Obito sensed the build up of chakra in Sasuke's eyes. But with Sharingan because in case of Pain when Yahiko met Tsunade, he saw the chakra covering their feet.