A method for warning a user of a head-mounted display of potential collisions with real-world obstacles, comprising the steps of: defining a location of said obstacles relative to a reference point; continually monitoring a location of said user relative to said reference point; performing a first detection to determine when a first distance between said location of said user relative to a location of one of said obstacles is smaller than a predetermined alarm threshold; and in response to said first detection, displaying a visual alarm on said head-mounted display to provide an indication to said user of a potential collision with said one of said obstacles; continually monitoring a location of an object held by said user , performing a second detection to determine when a second distance between said location of said object relative to said location of said one of said obstacles is smaller than said predetermined alarm threshold, and, in response to said second detection, displaying a visual alarm on said head-mounted display to provide an indication to said user of a potential collision between said object and said one of said obstacles, wherein the step of defining said location of said obstacles relative to said reference point further comprises prompting said user to walk around a portion of boundaries of a real operating space while holding said object, and detecting said location of said object at a plurality of points in time during an execution of said step, and wherein, if said second detection determines that the second distance between said location of said object relative to said location of said one of said obstacles is smaller than said first predetermined alarm threshold, said visual alarm increases in intensity as said object gets closer to said one of said obstacles. defining a location of said obstacles relative to a reference point; continually monitoring a location of said user relative to said reference point; performing a first detection to determine when a first distance between said location of said user relative to a location of one of said obstacles is smaller than a predetermined alarm threshold; and in response to said first detection, displaying a visual alarm on said head-mounted display to provide an indication to said user of a potential collision with said one of said obstacles; continually monitoring a location of an object held by said user , performing a second detection to determine when a second distance between said location of said object relative to said location of said one of said obstacles is smaller than said predetermined alarm threshold, and, in response to said second detection, displaying a visual alarm on said head-mounted display to provide an indication to said user of a potential collision between said object and said one of said obstacles, wherein the step of defining said location of said obstacles relative to said reference point further comprises prompting said user to walk around a portion of boundaries of a real operating space while holding said object, and detecting said location of said object at a plurality of points in time during an execution of said step, and wherein, if said second detection determines that the second distance between said location of said object relative to said location of said one of said obstacles is smaller than said first predetermined alarm threshold, said visual alarm increases in intensity as said object gets closer to said one of said obstacles. <EOS>