Gyroscope.gravity

Description

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

using UnityEngine;

public class Example : MonoBehaviour
{
    float movementScale;

    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;
    }
}