The only part of Zetsu that was known to sense things was Black Zetsu. Black Zetsu can sense beings just like any other sensor, but its range is quite impressive as it sensed Naruto and B almost immediately after leaving the Self-Repairing Barrier on Genbu. It also was capable of sensing the chakra of Asura and Indra within their respective hosts, which is how it knew who to target to get to try and awaken the Rinnegan.