Device: ASUS ROG Phone 3 (ZS661KS) Prerequisite: USB Debugging (optional, for advanced commands) Difficulty: Easy Risk Level: Low (no data loss) 1. Abstract Fastboot Mode is a diagnostic and firmware-flashing protocol used on Android devices. On the ASUS ROG Phone 3, Fastboot is essential for unlocking the bootloader, flashing custom recoveries (e.g., TWRP), sideloading OTA updates, or restoring factory images. This paper outlines the two reliable methods to enter Fastboot Mode: hardware key combination and ADB command. 2. Method 1: Hardware Key Combination (No PC Required) This is the primary method when the device is powered off or unresponsive.