This document provides a comparative study of existing intrusion detection systems for smartphones. It discusses 5 different intrusion detection approaches: 1) a cloud-based anomaly detection system, 2) a signature-based host-based IDS, 3) a rule-based host-based IDS called AMOXID, 4) an anomaly-based behavioral detection framework called Andromaly, and 5) an anomaly-based cloud-based detection system. It provides an overview of each approach and compares them based on parameters like detection method, positioning, type of analysis, alerts, scalability, pros, and cons. The conclusion is that combining anomaly and signature-based detection could improve attack detection performance for smartphones.