Gyroscope.gravity

Description

Returns the gravity acceleration vector expressed in the device's reference frame.

This property returns Vector3.zero until the device delivers its first motion sample after the gyroscope is enabled. Read the gravity vector on a later frame, after the sensor has produced data.

using UnityEngine;

public class Example : MonoBehaviour
{
    float movementScale;

    void Start()
    {
        Input.gyro.enabled = true;
    }

    void Update()
    {
        // A "spirit level" - the dot product of the gravity and the Y axis (ie, Vector3.up)
        // is a measure of how far the device is from level on that axis (it will be zero
        // if the device is perfectly level). This value can be used to position an object
        // to act as the "bubble".
        Vector3 pos = transform.position;
        pos.y = Vector3.Dot(Input.gyro.gravity, Vector3.up) * movementScale;
        transform.position = pos;
    }
}