I had this thought about monowire as a defensive weapon when I found it.
Current snipers sometimes use this trick when shooting from a building, but it can be employed by almost anyone.
Snipers will string a single line of fishing wire, at about 4.5' off the ground, across one or more doorways that leads to their position.
It is at neck height for 2 reasons, one; to slice the neck of someone moving quickly through the door and 2; so the sniper knows they can move through the house freely if they keep low.
If you did this with monowire, it would be even more deadly, as it's harder to see, and cuts easier.
You wouldn't have to stop at one string with monowire, string 4 or five up and turn the first person who comes through into mince meat...