Help with vulnerable adult

[Daisymclazy]

Hi, sorry I am unashamedly posting here for traffic. If anyone can suggest a better board I'll happily get it moved.
A friend has recently been moved to temporary, emergency accommodation. He has a code to enter the main door and a code to enter his own door. He is unlikely to be able to memorise these codes. Currently he is carrying a piece of paper with the codes and consulting it at each door. The other people in the building may not all be nice. Has anyone an idea of how he could keep these codes accessible to him but not easily read over his shoulder/ not wasting time outside the doors looking at them?
I feel like there's an easy solution but can't think what it might be. Any ideas will be much appreciated. Thanks in advance.

Could he get a swipe card? Or anything like this what does security use?

Does he have a phone, because no one will care or notice if he is using it to keep track of the numbers

I write numbers as phone numbers - like the last 4 digits are the pin number, for example.
So if someone finds it, it is slightly harder to work out what it is. I can save them in my phone rather than writing them on paper.

Or you remember it like a story, but that demands a certain type of brain. But for example 9 ducks were in one pond. Three girls came and gave them seven breadcrumbs. 9137

@cduffs no swipe card available. @redshoeblueshoe, love your username, I've gone out in odd shoes before. He has a phone but can not yet operate it with any confidence. We've been practicing with the phone but he's a bit hit and miss. There must be a genius solution...

@superloudpoppingaction that might work.. I'm seeing him tomorrow so we'll try that. Any other suggestions most welcome, this is all new to me, I've known him a while but had no idea his previous situation was so bad. He's very vulnerable and potentially an easy victim.

A small engraved disc on a chain that he could wear facing backwards to hide the code from others?

Might sound stupid but a small combination lock with the number visible for him in a zip pocket in his bag?

Thank you @teabagsgalore and @catnamechange101, both good options to explore.

Could he write it on the inside of his arm/wrist. It's cold weather so everyone is wearing long sleeves.

Would something like 2 different shaped dog tags work with the codes engraved on them like dates eg. 13/04/'22 or, if he can figure it out, 13 April '22.?
Could have a round shaped one for the main door and a bone shaped one for his own door?

Do the people that run the building have the facility to change the codes? If so, maybe they could alter the one for his front door to a number that he can remember like his birthday.