1. An input device for a finger touch interface, comprising: a magnetic unit worn on a tip of a user's thumb for establishing a magnetic field; at least a first magnetic field sensing unit worn on a tip of any finger except the thumb, wherein the first magnetic field sensing unit includes a first substrate and a plurality of first sensors mounted on the first substrate; and at least a second magnetic field sensing unit worn on a segment of any finger except the thumb, wherein the second magnetic field sensing unit includes a second substrate and a plurality of second sensors mounted on the second substrate; wherein the first sensors or the second sensors are configured to be used as an input area to detect magnetic flux density of the magnetic field while the user's thumb interacting with the input area so as to generate a first signal indicating a position of the magnetic unit relative to the first or second magnetic field sensing unit or a second signal indicating movement of the magnetic unit relative to the first or second magnetic field sensing unit.