AlarmClock.cs

using UnityEngine;

public class AlarmClock : MonoBehaviour
{
	const string ACTION_SET_ALARM = "android.intent.action.SET_ALARM";
	const string EXTRA_HOUR = "android.intent.extra.alarm.HOUR";
	const string EXTRA_MINUTES = "android.intent.extra.alarm.MINUTES";
	const string EXTRA_MESSAGE = "android.intent.extra.alarm.MESSAGE";

	public void OnClick()
	{
		print("Hello!");
		CreateAlarm("My alarm!", 8, 52);
	}

	public void CreateAlarm(string message, int hour, int minutes)
	{
		var intentAJO = new AndroidJavaObject("android.content.Intent", ACTION_SET_ALARM);
		intentAJO
			.Call<AndroidJavaObject>("putExtra", EXTRA_MESSAGE, message)
			.Call<AndroidJavaObject>("putExtra", EXTRA_HOUR, hour)
			.Call<AndroidJavaObject>("putExtra", EXTRA_MINUTES, minutes);
		
		GetUnityActivity().Call("startActivity", intentAJO);
	}

	AndroidJavaObject GetUnityActivity()
	{
		using (var unityPlayer = new AndroidJavaClass("com.unity3d.player.UnityPlayer"))
		{
			return unityPlayer.GetStatic<AndroidJavaObject>("currentActivity");
		}
	}
}