A portable electrical device includes a shell, a display device, a power management device, a touch button positioned on the shell, and a conductive substrate positioned inside the shell. The conductive substrate is spatially corresponding to the touch button and spaced apart a predetermined distance from the touch button. When a force is applied by a users finger to push the touch button to touch the conductive substrate, the power management device provides a predetermined subtle alternating current to the users finger to test a body fat percentage of the user and the display device displays the body fat percentage.
