All parts used in this post can be gotten from www.nerdshed.com.ng with a pay-on-delivery option.

Ever heard of Tesla? The autonomous cars (no drivers) produced in the US owned by Elon Musk. These are able to perform without drivers with the help of ultrasonic sensors which measures distances between it and other objects. These sensors are really cheap and can be incorporated into your project with an Arduino. Think of building a device that alerts you if someone enters your room/office, or an autonomous model car. Anything atall. This guide will put you through in building one. http://blog.nerdshed.com.ng/2017/09/14/measure-the-distance-with-hc-sr04/