The iPhone has a few different sounds you can use for the alarm. Back when I had one I used to have to switch it out from time to time as I got used to them. That might help, but like the others have mentioned using autosuggestion is a great tool. Set the intention to wake up and give yourself a specific time, such as “I will wake up in 5 hours from right now.” Imagine yourself doing, make it clear that it will happen.
It’s like telling yourself “oh, I’ll get the chicken out of the oven in an hour.” Just make it something that is going to happen and you are going to remember. The human mind is very powerful, and if you can get autosuggestion down it will really help in your quest for LD’s.
I’d suggest you read this article and its follow up which is found here. Great guides on setting intentions.