An electronic device includes air input sensors that gather air input from a user's fingers, a stylus, or other object in a volume of air near the electronic device. The air input sensors include ultrasonic transducers that emit ultrasonic signals towards the volume of air and that detect the ultrasonic signals after the signals reflect from the external object. Using time-of-flight measurement techniques, control circuitry tracks the movement of the external object in the volume of air near the electronic device. A display provides visual feedback of the air input, such as shadows that preview where the input will be directed to on the display. The volume of air where input is detected is divided into multiple input zones that trigger different actions from the electronic device. The ultrasonic transducers include acoustic lenses.