A smartphone, comprising: a touch display, and a radar system, implemented at least partially in hardware, configured to: provide a radar field; sense reflections from a human body part of a user in the radar field; analyze the reflections from the human body part in the radar field; and provide, based on the analysis of the reflections, radar data; the smartphone further comprising one or more computer processors; and one or more computer-readable media having instructions stored thereon that, responsive to execution by the one or more computer processors, implement a radar-based application configured to: present an augmented-reality, AR, element through the touch display of the smartphone, the AR element including a touch input control and related to a real object, an image of the real object being presented through an image-capture device on the touch display; and responsive to a determination, based on the radar data, that the human body part in the radar field is moving toward the touch display, maintain the touch input control at a fixed location on the touch display, even if the image of the real object is no longer presented on the touch display due to a movement of the smartphone. a touch display, and a radar system, implemented at least partially in hardware, configured to: provide a radar field; sense reflections from a human body part of a user in the radar field; analyze the reflections from the human body part in the radar field; and provide, based on the analysis of the reflections, radar data; the smartphone further comprising one or more computer processors; and provide a radar field; sense reflections from a human body part of a user in the radar field; analyze the reflections from the human body part in the radar field; and provide, based on the analysis of the reflections, radar data; the smartphone further comprising one or more computer processors; and one or more computer-readable media having instructions stored thereon that, responsive to execution by the one or more computer processors, implement a radar-based application configured to: present an augmented-reality, AR, element through the touch display of the smartphone, the AR element including a touch input control and related to a real object, an image of the real object being presented through an image-capture device on the touch display; and responsive to a determination, based on the radar data, that the human body part in the radar field is moving toward the touch display, maintain the touch input control at a fixed location on the touch display, even if the image of the real object is no longer presented on the touch display due to a movement of the smartphone. present an augmented-reality, AR, element through the touch display of the smartphone, the AR element including a touch input control and related to a real object, an image of the real object being presented through an image-capture device on the touch display; and responsive to a determination, based on the radar data, that the human body part in the radar field is moving toward the touch display, maintain the touch input control at a fixed location on the touch display, even if the image of the real object is no longer presented on the touch display due to a movement of the smartphone.