What are you afraid of?  What causes that fear?  If you can stop and analyze those two questions you are well on your way to the conception of an invention.  If you know the cause of fear, then you can invent something that can keep you safe from that fear.  Are you afraid of the dark?  What can you do to insure you are never in the dark?  Are you afraid of snakes?  What can you do to make sure your home stays snake free?  As the old saying goes: “Necessity is the mother of invention”.  When you have a need, you can work it out.