Well, let's suppose I was called to fix a computer problem and went to your house. I might or might not have gotten the address right.
I knock on the door and it opens slightly. It wasn't closed tightly. I just go ahead and push it open and enter, just standing in the doorway.
I've been making housecalls for a long time and I can tell a lot from here, like if there's a big scary dog and who is home, man, woman, child or more than one person, by the kind of voices and sounds I hear. What I hear makes me smile. You're alone in the next room on the phone. And no dog is at the door greeting me.
I close the door quietly and wait for you to hang up and then walk into the room where you are. "Hello I'm here to fix your security system" I say.
Of course you're startled. This is your house and you thought you were alone. You say "How, how..."
I tell you "The front door was open so I came in. I hope you're not frightened."
This is very convenient for me. You're wearing a robe with a towel on your head, so there's either panties or nothing underneath. And to top it off you're sorting laundry.
As you start to tell me you don't have a security system I grab a handfull of washrags and say "Let's see your bedroom". A couple of times you start to say something but I am a lot bigger than you and it's clear this is going to happen.
In your bedroom I tell you to lay on the bed. Robe on is OK with me. I unplug the phone and move it. I've got a coil of nylon rope in my bag and take it out. First I wrap one of your washcloths around your wrist, then tie the rope. Then the rope goes around the post of your bed and around your other washcloth-covered wrist. Around the post and down to the post at the foot of the bed, and your ankles are bound the same way. Now you're spreadeagled on your bed.
"Are you OK" I ask you.