According to an embodiment, an activity tracker includes an acceleration sensor capable of detecting accelerations in directions of two or more axes orthogonal to each other, an arm motion determination unit configured to determine on the basis of an output from the acceleration sensor whether there is a predetermined motion within a predetermined time period, when operation of an operation button is detected, and a transmission processing unit configured to cause a lamp to glow and wirelessly transmit a piece of corresponding information corresponding to the predetermined motion and a piece of time information at a time of detecting that there is the predetermined motion, when it is determined by the arm motion determination unit that there is the predetermined motion.
