An electromagnetic (EM) pose tracking system includes a computer input device having a pen or stylus form factor. In some embodiments, a base station device includes one of the transmitter (Tx) or receiver (Rx) module for the EM pose tracking system while the computer input device includes the other of the TX and receiver modules. The EM pose tracking system employs the Tx and Rx modules to collect EM pose data indicating a relative pose between the Tx and Rx modules. Based on the EM pose data, the EM pose tracking system (or a computer device working with the EM pose tracking system) identifies a pose (position, orientation, or both position and orientation) of the computer input device.