1. A processor-implemented method for detecting motion in a 3-D depth camera, comprising the processor-implemented steps of: obtaining acceleration readings for x-, y- and z-axes from a three-axis accelerometer in the 3-D depth camera at successive time points, and for each time point: obtaining short and long term running averages of the acceleration readings for each axis of the x-, y- and z-axes, where x-axis long average, y-axis long average and z-axis long average are the long term running averages of the acceleration readings for the x-, y- and z-axes, respectively, and x-axis short average, y-axis short average and z-axis short average are the short term running averages of the acceleration readings for the x-, y- and z-axes, respectively; obtaining differences between the short and long term running averages of the acceleration readings for each axis of the x-, y- and z-axes; obtaining absolute values of the differences for each axis of the x-, y- and z-axes, where |x-axis long average−x-axis short average| is the absolute value of the differences for the x-axis, |y-axis long average−y-axis short average| is the absolute value of the differences for the y-axis, and |z-axis long average−z-axis short average| is the absolute value of the differences for the z-axis; obtaining a sum from: |x-axis long average−x-axis short average|+{scaling factor x |y-axis long average−y-axis short average|}+|z-axis long average−z-axis short average|, where 0<scaling factor<1 and the y-axis is a vertical axis, so that movement in the vertical axis is attenuated relative to movement in the x or z axis; determining if the sum exceeds a threshold level; if the sum exceeds the threshold level, providing an indication that movement of the 3-D depth camera is detected; and if the sum does not exceed the threshold level, providing an indication that movement of the 3-D depth camera is not detected.