An embodiment of a device includes at least one sensor, a determiner, and a notifier. The at least one sensor is configured to be located on a body portion of a subject and to sense an object. The determiner is configured to determine, in response to the sensor, whether the body portion may contact the object. The notifier is configured to notify the subject in response to the determiner determining that the body portion may contact the object. Such a device (e.g., attached to, or part of, a shoe) may be useful to warn a subject of a potential collision between an object (e.g., stairs, furniture, door jamb, curb, toy) and a body part (e.g., foot, toes) in which the subject has lost feeling, the ability to feel pain, or proprioception. And such a warning may help the subject to avoid inadvertently and repeatedly injuring the body part.