Careful Driver is an excellent tool to help you drive safely. It will help you stay under a speed you specify, and hopefully help you gain good driving habits.
Careful Driver uses GPS to determine speed and measures a sustained speed for a reasonable period of time. It then checks this speed against a user-defined speed limit, a driver-imposed limit on how fast they want to drive; and if the measured speed is more, will notify the user in a variety of user-specified ways. It has an infinitesimal false positive rate and a low missed negative rate, and doesn't use a lot of battery life. Furthermore, almost all errors are due to errors in GPS and not the program and algorithm used. It can notify the user of a speeding violation by vibrating, showing a message in the status bar, or playing a voice alert. It also can send a text message to anybody notifying them if you go too fast.
Careful Driver does not send any private information outside of the phone, except a text message to the number(s) you have selected in case of speeding violations, and to translate your location using Google's services.
This application is intended only as an aid. We are NOT responsible for any accidents or problems that result from use or misuse of this application. WE ARE NOT LIABLE FOR ANYTHING. Furthermore, this application can not determine whether or not you are the driver of the car you are in, and will continue to function even if you are a passenger.