On the show Daredevil, various characters associated with the group known as the Hand have demonstrated certain skills of concealment, namely

the ability to hide from Daredevil's enhanced senses.

However, apparently Daredevil can still

sense the location of their swords. However, they are apparently not invisible, since Elektra can see them.

Matt has various enhanced senses, such the ability to hear very faint sounds or sense air currents, all of which help him build a reasonably accurate picture of the location of his enemies. So

• What senses does Daredevil normally use to perceive opponents?
• What senses does Daredevil use to detect the location of the ninjas' swords (but not, say, their clothing)?

And of course,

• How do the assassins hide from these senses in a way that is consistent with Daredevil being able to perceive the location of most objects?