Abstract: A portable device configured to detect vertical changes in a surrounding of a moving person, wherein the portable device comprises: a housing; an optical depth sensor; a processor operative to: receive data from the depth sensor; process the data received; identify, based on the processed data, any vertical change that is present in the field of view of the optical depth sensor, and determine whether an identified vertical change forms a potential hazard to the moving person; and a warning generator for generating an indication to that person, upon determining that an identified vertical change forms a potential hazard to the moving person.