Undismissable alarm

I’m quite a heavy sleeper and I’m very hard to wake up. If I set up capthas for the alarms I get used to them and I start solving them in sleep. What would help me greatly would be an undismissable alarm (just set a duration).

I generally use Spotify as my alarm on my Bluetooth speakers turned up quite loud, and after eg. 5 minutes of that you can be sure I will be awake.