On the Holiday you put in 4 numbers. Just make sure you remember the numbers or you will have to have someone from the pursers desk come open it. The room steward can't reset the safe. It is convenient to have a safe that you enter numbers because everyone in the room can be given them. The safes that need a magnetic card entails leaving the card out in the room so everyone can have access to it.
And yes, on the Holiday there is a separate card for the door not the sign and sail card.
On the Jubilee you have to obtain a key from your room steward. Make sure you don't lose it as there is a charge of $40 if you do.
I wouldn't suggest using your sail and sign card's magnetic strip for your safe....use a credit card if you have one. We closed out a credit card a few years back and I keep the old cards for use when on ships with that kind of safe.
If you have an old credit card, that is the best "key" for the safe's. It works with the magnetic strip, that's why I suggest using an old or expired card. That way it cannot be duplicated, and it gets damaged, no great loss.