This book constitutes the thoroughly refereed post-conference proceedings of the 12th International Conference on Mobile Computing, Applications, and Services, MobiCASE 2021, held in November 2021. The papers are organized in two topical tracks: mobile application and deep learning, and mobile application with data analysis.

Mobile Application and Deep Learning.- YOLO-RFB: An improved traffic sign detection model.- Privacy-Preserving Sharing of Mobile Sensor Data.- Service performance analysis of cloud computing server by queuing system.- CLES: A Universal Wrench for Embedded Systems Communication and Coordination.- When Neural Networks Using Different Sensors Create Similar Features.- Mobile Application with Data Analysis.- Improving Togetherness Using Structural Entropy.- Blockchain-based Group Key Agreement.- Attacking community detector: a way to mislead detector via manipulating the graph structure.- ResNet-like CNN Architecture and Saliency Map for Human Activity Recognition.