You only need to figure out one Resident Evil 3 safe code in the demo, but it can still be an easy one to miss. The previous game in the remastered lineup was full of them, so make sure you've ticked them all off in our Resident Evil 2 remake lockers and safe codes guide.
Since we've only got a short 20-minute demo to play so far, there's only one safe we need to bust into. It's fairly easy to find given the linearity of this zombie-filled gameplay snapshot, but I'm going to break down where you can find your locked loot, and the Resident Evil 3 safe code you need to access it.
Resident Evil 3 remake safe code solution
You should find the safe you're looking for about halfway through the demo. On the main street, head up the stairs to the first floor of Moon's Donuts. Turn left and carry on until you reach the next building. The safe should be nearby.
The Resident Evil 3 safe code is: 9 left, 1 right, 8 left.
If you want to know how you get to that solution, you start with the Drugstore Owner's Manual to the left of the safe. It mentions that the code is associated with the 'Aqua Cure queen'. This refers to a poster with 'Aqua Cure' on it, and the code, which is found in the Redstone Pharmacy on the street opposite the building with the safe.
Your reward is a dot sight for your handgun. While that is useful, you won't be using it all that long. Either way, it'll make popping the skulls of the shuffling horde that bit easier.