This is a paid asset, but now you can download 3D Field of View for FREE, but please remember this package is provided only for learning purposes or to be able to test before buying the product, NOT FOR COMMERCIAL PURPOSES.
Detail this asset from Unity Store: Original Link
3D Field of View v1.1
3D Field of view is a package to designed to give your AI Vision.
“3D Field of View” is an engine designed to allow sight in more than a flat plane. It is designed to be highly customizable, and easy to integrate with other projects. Included are different demos showing distinct usages of the system, For further support, you can contact the developer directly either through Discord or the Unity Forums. Supports the following render pipelines: Standard, SRP LW and SRP HD. Compatible with Unity 2019.4.9 and above