Personal Force Field

Are you bothered by strangers standing too close to you? When I was a child I learned about the "magic bubble". This was an area three feet around all of your body that no one was allowed to enter unless invited. If you hate people that you don't know standing close enough to you that you can smell their breath, this is the device for you. Auto alarm companies have already used this technology in devices that warn you that you are standing too close to the vehicle with an automated voice that tells you so. Why not have the same warning for personal space. A device that you can wear that will give a verbal warning that says "You are standing too close to me. Back up." You could switch it off for elevators or other situations where you would expect to be crammed in with other people, but if you are standing waiting for the crosswalk light where there is plenty of room, there is no reason for someone to be rubbing up against you. This would be a handy device for that situation. If they don't back off within an amount of time specified by the user, the device would deliver a mild electric shock as a warning.