How can I detect if the phone is looking down?

Well I did once make a spirit level using a Gyroscope, which works on the x-axis and z-axis of your device. There are multiple ways of checking for screen orientation in world space. It's how your phone knows to turn portrait and landscape when tilted:

• You could use the accelerometer, for example, on one of the axis to work out how tilted it is.

• As well as the Gyroscope, which I'm going to use for this example.

  ---

  Gyroscope Bubble Level

To create a bubble level that can detect whether your phone is flat (meaning facing directly up or down), you would need the gyroscope readings on the x-axis.

For example:

 public class Gyroscope : MonoBehaviour
 {
     private UnityEngine.Gyroscope gyro; // Gyroscope
     private Quaternion rot; // Base quaternion to get a rotation
 
     private void Start()
     {
         EnableGyro();
     }
 
     private void EnableGyro()
     {
         if (SystemInfo.supportsGyroscope)
         {
             gyro = Input.gyro;
             gyro.enabled = true;
             rot = new Quaternion(0, 0, 1, 0);
         }
     }
 
     private void Update()
     {
         transform.localRotation = gyro.attitude * rot;
         transform.eulerAngles = new Vector3(transform.eulerAngles.x, 0, 0);
 
         // The value 'transform.eulerAngles.x' 
         // is your phone's orientation on the x-axis
     }
 }

I have some more code for working out how straight your phone is on the z-axis as well, but that's for another day. You might want some text to display your orientation value, and assume a range where you can safely say that if the phone's x-angle is inbetween these two values, it is facing down.

Hope you get it to work @foghunt