A tracking detection and alarm method which is applied to a navigation device use a number of positioning data points retrieved from a navigation module of the navigation device. A number of deflections and a number of average speeds that correspond to the position data points are calculated and generated. A number of maximum deflections are calculated and generated according to the average speeds. When a deflection of a positioning data point is greater than a maximum safe deflection thereof, one is added to a frequency of unsafe driving instances. When the frequency of unsafe driving instances is greater than a preset threshold value, an unsafe driving alarm is activated.