Input.anyKeyDown

説明

ユーザーがなんらかのキーかマウスボタンを押した最初のフレームのみ true を返します（読み取り専用）

You should be polling this variable from the Update function, since the state gets reset each frame. It will not return true until the user has released all keys / buttons and pressed any key / buttons again. This does not detect touches. For touches, use Input.touchCount.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    void Update() {
        if (Input.anyKeyDown)
            Debug.Log("A key or mouse click has been detected");
        
    }
}