Caution! is the word

There was an unexpected knock on my door, and as I
always do I first opened the peephole and asked,
"Who's there?" "UPS, ma'am. I have a package that
needs a signature."
"Where's the package?" I asked suspiciously.
The delivery man held it up.
"Could I see some ID?" I said, still not convinced.
"Lady," he replied wearily, "if I wanted to break
into your house, I'd probably just use these." And
he pulled out the keys I had left in the door.