A few recent posts discuss mirrors for signalling if trapped in a car. Our retired CHP officer, old bald guy and I have both been involved in searches for vehicles that have gone over the side. Some of our canyons in California are so deep and covered in dense chapparel the best of mirrors are hindered. A portable, self powered emergency horn such as those used on small boats is a good idea. Like any limited life unit, make sure somebody is listening. Sometimes a car can be completely hidden. Our periodic brush fires always reveal a vanished motorist from the past.