Let users send feedback through App to your email ID so that you can directly improve your app.

More detailed information about metal detector data. Example: "closer to metal"

Let the user keep track of the stats shown by the sensor by being able to save the value with respect to time in a list below the sensor.
This can be implemented by using a Local DB & creating tables with respect to sensors.
This feature won't be applicable to all sensors.

Don't put all types of sensors in the navigation drawer.
Don't open a default sensor when the app launches.
The user should be able to select which sensor he want to explore from the start i.e. all sensors should be visible from the start with its icon to select.

Use LiveData and handle device rotation.

Use view models

Only show sensors that are available in that particular device, because showing extra sensors which won't work on that device will only demotivate the user to use that app.

Green for safe
Red for danger

Tell the user if the current metal value is safe for humans to be around or not.

com.google.android.play:core has added this note for core:1.10.3:

Update your Play Core Maven dependency to an Android 14 compatible version! Your current Play Core library is incompatible with targetSdkVersion 34 (Android 14), which introduces a backwards-incompatible change to broadcast receivers to improve user security. As a reminder, from August 31, Google Play requires all new app releases to target Android 14. Update to the latest Play Core library version dependency to avoid app crashes: https://developer.android.com/guide/playcore#playcore-migration

You may not be able to release future versions of your app with this SDK version to production or open testing.

In-App review's toast message is not appropriate
If the user opens an in-app review and doesn't give a review then when the user visits the in-app review again "Review successful" toast message popups up without giving a review.