I have a pre-paid one from T-mobile. Only costs $10 a year to keep it active after I initially paid $100 several years ago. I've used it several times to phone in other people's emergencies and weird things like a horse in the road. I occasionally use it to call my wife if I will be late so she won't worry. I have twice used it to call the police when motorists were harassing me. This did have the effect of getting the motorists to back off. I think you should carry one just in case you are seriously injured and still conscious so you can dial 911 for an ambulance. I also think it is a good idea as a harassment deterrent.