More and more mobile devices, such as smartphones and pad/tab devices, are being used in IEEE 802.11 Wireless LANs (or Wi-Fi). However, mobile users are currently unsatisfied with using Wi-Fi on the move due to large handoff delay. In order to perform fast handoff, this paper proposes a new scheme using a geomagnetic sensor (or a digital compass) embedded in mobile devices. The proposed scheme predicts the direction of movement of a Mobile Station (MS) from the currently associated Access Point (AP) and performs active scanning with a reduced number of channels. The proposed scheme was implemented in Android smartphones and their performance was evaluated in a real indoor WLAN environment. Our test results show that the proposed scheme reduces handoff delay compared to conventional handoff and selective scanning scheme. In addition, the proposed scheme does not require modification to existing APs, which makes it very practical for using real-time multimedia services on current mobile devices.