I search an activity tracker wich allow to access to the hardware ?
I want to get the accelerometer raw data to save the body movement of the user.
I've tested several of today's popular fitness trackers and have not come across one that will broadcast realtime accelerometer / gyro data. You will find apps that can do this using the phones builtin in sensors.
This would be fairly easy product to roll your own with a Arduino + BLE + Accel/Gyro. Making it a comfortable wearable could be challenging. If I were to make one I'd use the following:
Processor: Adafruit Flora BLE and the LSM9DS0 (accel+gyro)
Checkout these other two DIY Arduino examples which are getting raw accelerometer data:
Hexoskin collects accelerometer data, but I don't think that data broadcast via Bluetooth.