latchkey
/ˈlætʃki/Definitions
1. noun
A child who is left to take care of themselves when they arrive home from school because their parents are not there.
“The latchkey kid walked in the front door, dropped her backpack, and headed straight for the fridge.”
2. noun
A small metal device that fastens a door or gate, often used in combination with a key.
“She turned the latchkey and swung open the heavy wooden door.”