This application provides a prompt method, applied to a portable device adsorbed on a magnetic holder. The method includes: a display of the portable device being off; and detecting, by the portable device, that a parameter related to a magnetic induction intensity deviates from a preset threshold range, lightening the display of the portable device when, before, or after outputting a voice prompt, and displaying, on the display, prompt information about moving the portable device. By using this method, a user can learn, in time, that the adsorption of the portable device on the magnetic holder is unstable, and move the portable device based on the prompt information, so that the portable device can be stably adsorbed on the magnetic holder, thereby effectively preventing the portable device from sliding down from the magnetic holder.