An embodiment of a device includes a sensor and a communicator. The sensor is configured to be attached to a body portion of a subject, to sense an object, and to generate information related to the object. The communicator is configured to provide the information to a determiner-notifier that is configured to determine, in response to the information, if the body portion may contact the object, and to generate a notification in response to 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.