There are times in an emergency where being very visible is good and other times when being invisible are a must. In both cases smoke bombs can be a real lifesaver. A few small colored (red, yellow) smoke bombs carried in your field (e.g. hunting, hiking, fishing, etc.) survival kit can bring help to you if you are lost or injured. In an urban situation a few smoke bombs set in cans (to prevent a real fire) can create the impression of a fire to discourage looters and even real arsonists from entering a building. Smoke screens have been used by the military for centuries. Two or three smoke bombs thrown out to screen an area you must cross or a person that must be rescued can keep you from being a target. Smoke bombs burn only a few (1 to 3) minutes and you must carefully consider the wind direction, wind velocity and timing. A wind shift that puts you in front of the smoke can silhouette you for a shooter. How many smoke bombs you have will be dependent on what kinds of situations you anticipate and what areas you may need to get through. The colored rescue signal smoke bombs are available in boating and sports stores. Around the Fourth of July smoke bombs can be purchased at any fireworks stand. I always carry these in my survival pack.