The woman was seen glancing nervously down the street.
Cops in Texas are baffled by the mystery of woman seen on security footage in shackles and desperately ringing doorbells in the middle of the night.
Authorities are now trying to identify the woman and determine whether her life is at risk.
She rang the bell at a house in Montgomery, located outside Houston, at 3:20 a.m. Friday.
The woman, barefoot and wearing a T-shirt, appears to have restraints on her wrist.
After ringing the bell, she glances nervously down the street. Then, she's gone.
Home security cameras have recorded numerous bizarre incidents of strangers ringing the bell or knocking, often late at night.
A recent situation involved a woman furiously rattling the door and banging on the window of a home in Fresno, California, after midnight.
In that case, the homeowner, a retired cop, pulled a gun and called 911.
Five days ago, a woman in Toronto was seen ringing a doorbell, but nobody came to her aid as a man dragged her away by her hair.
Security expert Steve Kardian explained what to do should someone ring your bell in the middle of the night.
"First of all, make sure you go to the door with cellphone in hand, get a picture of what is going on the other side of that door, dial 911 if that person really is in distress and then direct them to go to the side of the house, back of the house, or hide behind something for concealment because if they are being pursued, they won't be seen," he said.
Karidan says it's important not to let the person in your home.
"Look for body language, look for other people, but don't open that door right away," he advised.