A tracker, comprising: a body having a receiving space and a through hole, with the through hole being in communication with the receiving space, the body having two ends forming a pivoting portion and a first engaging portion, respectively, the body having a first electrically conductive portion and a second electrically conductive portion disposed in the receiving space; a movable element with an end pivotally connected to the pivoting portions of the body and another end having a second engaging portion corresponding in position to the first engaging portion of the body, wherein the second engaging portion and the first engaging portion of the body are engaged with each other and fixed to each other as soon as the movable element is pivotally connected to the pivoting portions of the body; a circuit module disposed on a side in the receiving space of the body, the circuit module comprising a wireless positioning unit and a memory unit, with the wireless positioning unit adapted to track and locate the tracker, process related data, and store the data in the memory unit; a power source module disposed on another side in the receiving space of the body and having an end electrically connected to the second electrically conductive portion; and a switch disposed at the through hole of the body, wherein the switch is electrically connected to the first electrically conductive portion and the second electrically conductive portion when pivoted to a first position such that the power source module forms an electrical loop together with the first electrically conductive portion of the body through the switch and is electrically connected to an external supply power source. a body having a receiving space and a through hole, with the through hole being in communication with the receiving space, the body having two ends forming a pivoting portion and a first engaging portion, respectively, the body having a first electrically conductive portion and a second electrically conductive portion disposed in the receiving space; a movable element with an end pivotally connected to the pivoting portions of the body and another end having a second engaging portion corresponding in position to the first engaging portion of the body, wherein the second engaging portion and the first engaging portion of the body are engaged with each other and fixed to each other as soon as the movable element is pivotally connected to the pivoting portions of the body; a circuit module disposed on a side in the receiving space of the body, the circuit module comprising a wireless positioning unit and a memory unit, with the wireless positioning unit adapted to track and locate the tracker, process related data, and store the data in the memory unit; a power source module disposed on another side in the receiving space of the body and having an end electrically connected to the second electrically conductive portion; and a switch disposed at the through hole of the body, wherein the switch is electrically connected to the first electrically conductive portion and the second electrically conductive portion when pivoted to a first position such that the power source module forms an electrical loop together with the first electrically conductive portion of the body through the switch and is electrically connected to an external supply power source.