If it’s wireless, assume it’s insecure.
Don’t know what else to say.
Oversimplifying the issue doesn't really help. Wired connections can be quite insecure as well. Lots of serious intrusions and crimes have been committed over copper.
All security is a value/time tradeoff. If what you have is valuable enough, someone WILL gain access, given enough time. If what you have is of no value, nobody will try to get it even if it's public.
All you can do is make access difficult enough that it isn't worth the bad guy's time to get it.