A simple Unity Cheat Code system, optionally play a sound when a cheat code is used. Add cheats in the Inspector with UnityEvent, or through code using RegisterCheat method

CheatCodeDetector.cs

using UnityEngine;
using System.Collections.Generic;
using System;
using UnityEngine.Events;

[RequireComponent(typeof(AudioSource))]
public class CheatCodeDetector : MonoBehaviour
{
    [SerializeField] private List<Cheat> cheats = new List<Cheat>();

    private AudioSource audioSource = null;
    private Cheat cheatToRemoveThisUpdate = null;

    [Serializable]
    private class Cheat
    {
        public string cheatCode = string.Empty;
        [Tooltip("Optional")] [SerializeField] private AudioClip audioClip = null;
        [SerializeField] private bool deactivateCheatOnUse = false;
        [SerializeField] private UnityEvent onUseCheat = null;

        private Action onActivate = null;
        private int cheatTypeIndex;
        private CheatCodeDetector cheatCodeDetector = null;

        public Cheat(string cheatCode, AudioClip audioClip = null, bool deactivateCheatOnUse = false, Action onActivate = null, UnityEvent onUseCheat = null)
        {
            this.cheatCode = cheatCode;
            this.audioClip = audioClip;
            this.deactivateCheatOnUse = deactivateCheatOnUse;
            this.onActivate = onActivate;
            this.onUseCheat = onUseCheat;
            cheatTypeIndex = 0;
        }

        public void Update()
        {
            if (Input.inputString != "")
            {
                if (Input.inputString[0] == cheatCode[cheatTypeIndex])
                {
                    cheatTypeIndex++;
                    if (cheatTypeIndex == cheatCode.Length)
                    {
                        onActivate?.Invoke();
                        onUseCheat?.Invoke();

                        PlaySoundOnActivate();

                        if (deactivateCheatOnUse)
                            DeactivateCheatCode();

                        cheatTypeIndex = 0;
                    }
                }
                else
                {
                    cheatTypeIndex = 0;
                }
            }
        }

        private void PlaySoundOnActivate()
        {
            if (cheatCodeDetector == null)
                cheatCodeDetector = FindObjectOfType<CheatCodeDetector>();

            if (audioClip != null)
                cheatCodeDetector.PlaySound(audioClip);
        }

        private void DeactivateCheatCode()
        {
            if (cheatCodeDetector == null)
            {
                cheatCodeDetector = FindObjectOfType<CheatCodeDetector>();
            }

            cheatCodeDetector.RemoveCheat(cheatCode);
        }
    }

    protected void Update()
    {
        // We skip the update if we're removing a cheat so we don't get an error about
        // changing a list while we're iterating through it
        if (cheatToRemoveThisUpdate!=null)
        {
            cheats.Remove(cheatToRemoveThisUpdate);
            cheatToRemoveThisUpdate = null;
        }
        else
        {
            cheats.ForEach(x => x.Update());
        }
    }

    public void RegisterCheat(string cheatCode, Action onActivate, bool deactivateCheatOnUse = false, AudioClip audioClip = null)
    {
        cheats.Add(new Cheat(cheatCode, audioClip, deactivateCheatOnUse, onActivate));
    }

    public void RemoveCheat(string cheatCode)
    {
        var cheatToRemove = cheats.Find(x => x.cheatCode.Contains(cheatCode));
        if (cheats.Contains(cheatToRemove))
        {
            cheatToRemoveThisUpdate = cheatToRemove;
        }
        else
        {
            Debug.Log("Attempted to remove a cheat code that isn't currently available");
        }
    }

    public void PlaySound(AudioClip audioClip)
    {
        if (audioSource == null)
            audioSource = GetComponent<AudioSource>();

        if (audioSource != null && audioClip != null)
            audioSource.PlayOneShot(audioClip);
    }
}