@Irene866 As @Lisa723 suggests I would most definitely be changing the code between guests.
It helps to prevent all sorts of difficulties including early check in, guests popping back after checkout and potentially disrupting new guests, not to mention the obvious potential for burglary, theft etc.
It only takes a few minutes at most.
I personally usually make the code the first 6 digits of the guests mobile - the added bonus is it's easy for them to remember so unlocking is a breeze - they dont' have to scrabble about looking up the code
One of the best inventions ever IMO