Deer are surprisingly adaptable. A beep, tweet or honk may startle them at first, but they soon learn to ignore it and get back to foraging in your garden. A well-known PhD and garden author finally came up with a solution. This motion-activated device shines a bright light and plays an FM radio station you select. Because the sound is ever-changing, deer don't learn to ignore it. Human voices make them particularly nervous — talk radio is ideal.