3D Printing is a process for making a physical object from a three-dimensional digital model, typically by laying down many successive thin layers of a material. It brings a digital object (its CAD representation) into its physical form by adding layer by layer of materials. Like any other process, no matter how perfect we try to make them, defects do creep in. As such, defects like missing filament, abnormal printing etc. could be present in our product. This thesis describes the idea of finding defects during the ongoing process of 3D printing on each layer. The goal is achieved by developing a system to be attached to any open 3D printer with minimal interference on its functionality or parameters.