Physics.CheckSphere always returning false

I am trying to get Physics.CheckSphere to work, but it doesn’t seem to matter what layer mask I use or what radius I use, it never registers an object with a collider. I’m just trying to test the script out right now so my code is pretty simple.

public float radiusCircle = 2400f;
	public bool isSomethingThere = false;

	// Use this for initialization
	void Start () {
	// Update is called once per frame
	void Update () {

		if (Physics.CheckSphere (transform.position, radiusCircle, 1 << 12)) {
			isSomethingThere = true;
			Debug.Log("There is something there");

Ok, so I feel VERY silly for not noticing this before, but my colliders are 2D, but of course the checksphere only registers 3D colliders. So I slapped a 3D collider on my object, set the z-scale to 0 and it worked!
In the future, it might be helpful for the documentation to note what won’t work with 2D colliders since that might trip up newbies like me.