Trying to open a connection on the other hand it's like trying to open the door. That should be considered as a violation.
I'd strengthen pfundstein's claim; port scanning intrinsically works by trying to open connections. That isn't enough "like" any particular physical thing to make it a correct analogy; it isn't knocking, or walking in, or opening, or anything else. But one thing we can say, without using analogies, is that it is definitely an active effort, an action deliberately taken, not something passive like "looking" is in the real world. That is not on its own proof that it is wrong... I am merely saying, it is certainly active, not passive.
I'm referring to the literal, probably-hundreds-of-person-hours actions taken to create this functionality. This is relevant to both ethical and legal analyses. No analogy.
I think it comes under the Criminal Attempts Act 1981. But it might come down to whether you gather information, if you test a port, intending later - if successful - to attempt an exploit, then that seems like it could be unlawful (under the Law of England & Wales). Keeping a record of ports found with services could be sufficient to demonstrate intent.
[Just to be clear, I'm not endorsing/condemning the law here.]
What are the intents of people doing scan? I don't see any legitimate reason for scanning random people computers or servers that are not yours.
That sounds pretty suspicious to me. At least you need the consent of the house’s owner.
You might be doing a legitimate survey (as part of a locksmith business, say)?