Scanning detection, Single Packet Authorization

[Cezary Cieplinski]

Dear All,
I am new member here, also noob in OpenBSD.
And have some simple question.
Can you please tell me if there any technique to detect port scanning.
Is there any PF feature which I can use? Or any independent package similar to 
linux psad?
I am also interested in port knocking is there any support for it in OpenBSD.
I am looking for similar functionality like fwknop - Single Packet 
Authorization.
Best regards.