I often talk about hotel safety but it applies to any door you believe is secure. This week as many businesses are starting to return my travels meant that I stayed in 2 hotels.
As you can see from the pictures 1 door had the electronic lock operated by the door key and the other had that as well as a chain. Both had spy holes but one of which was blown so was too clouded to see through.
That means that any number of people could gain entry into your room.
I would always recommend those travelling to put a doorstop in your case to provide additional security and prevent anyone entering your room uninvited. It must be one of the cheapest and simplest methods of protecting yourself.