Loud noise is the best attention getter. The whistle is a proven internationally recognized call for help. The last thing a mugger wants is to have attention called to what he is doing. Keep it with you every time you walk, jog or ride your bike. Also great for camping. Each child and adult should have one to summon rescuers if they get lost. Use it to call the kids in for dinner. And of course they are always useful for teachers and referees at all kinds of sporting events. Length 2-1/2" Diameter 1/2". Quality, heavy duty key ring.