Корутина

    //Вариант№1
    private IEnumerator FadeIn()
    {
        _alarm.Play();

        while (_playerInAlarm && _alarm.volume < _maxVolume)
        {
            _alarm.volume += _fadeSpeed * Time.deltaTime;
            yield return null;
        }
    }

    private IEnumerator FadeOut()
    {
        while (!_playerInAlarm && _alarm.volume > 0)
        {
            _alarm.volume -= _fadeSpeed * Time.deltaTime;
            yield return null;
        }

        _alarm.Stop();
    }

    // Вариант №2.
    private IEnumerator ExecuteAlarm()
    {
        if (_playerInAlarm == true)
        {
            _alarm.Play();

            while (_alarm.volume < _maxVolume)
            {
                _alarm.volume += _fadeSpeed * Time.deltaTime;

                if (_playerInAlarm == false)
                    yield break;

                yield return null;
            }
        }
        else
        {
            while (_alarm.volume > 0)
            {
                _alarm.volume -= _fadeSpeed * Time.deltaTime;

                if (_playerInAlarm == true)
                    yield break;

                yield return null;
            }
        }

        _alarm.Stop();
    }