This study mainly concerns a safety device designed for child care. When children are out of sight or the caregivers cannot always pay attention to the situation, through the functions of this device, caregivers can immediately be informed to make sure that the children do not get lost or hurt, and thus, ensure their safety. Starting from this concept, a device is produced based on the relatively low-cost Bluetooth piconet system and a three-axis gyroscope sensor. This device can transmit data to a mobile phone app through Bluetooth, in order that the user can learn the situation at any time. By simply clipping the device in a pocket or on the waist, after switching on/starting the device, it will send data to the phone to detect the child’s fall and distance. Once the child is beyond the angle or distance set by the app, it will issue a warning to inform the phone owner.
 Teng, W. Y., Android Beginner Classes, 3rd edition, GOTOP Information, 11-2~11-15(2013).
 Huang, C. H., Gyroscope - from Tradition to Modern, Physics Bimonthly, 36, (3), 228-235 (2014).
 Chang, Y. C., Action Identification and of Mobile Phone Acceleration Sensor and Phubber Applications, the 12th Wang Hong Science Award Report (2013).
 Gasolin, Introduction to Android Mobile App Design, unified vitality Asset Management Limited Corporation, Article 1-5(2009).
 Shih, S. W., Arduino Micro Computer Applications and Pratice, Tiked Books, extended edition, Chapter 1, 2, 4, 7, 11, 15(2015).
 Chen, S. H., Arduino and the Bluetooth Communication of Arduino, Xuite, Arduino UNO+Bluetooth (2014).
 Android 4.3 (API level 18) introduces built-in platform support for Bluetooth Low Energy (BLE) in the central role and provides APIs that apps can use to discover devices, query for services, and transmit information.2014.
 Yeh, C. T., Lu, R. H., Gyroscope Principle and its Application, engineering and technology (2015).
 Huang, Y. L., Getting Started with Arduino: Read ADXL345 Triaxial Accelerometer, Digital Life, (2014).