The document presents a transparent developmental biometric-based system to protect user reauthentication using smartphones. It proposes a system called Safeguard that uses on-screen finger movements like sliding dynamics and pressure intensity as behavioral biometrics for accurate and efficient user verification. Safeguard first implements various machine learning approaches and selects support vector machine due to its high accuracy. It analyzes Safeguard's robustness against attacks and validates its efficacy through implementation on off-the-shelf smartphones with practical evaluation under different scenarios.