For some reason, seeing a deadbolt on a basement door really freaks me out.
"Kids, go downstairs and play! And stay down there!"
Yeah, I thought the same thing when we first bought the place 11 years ago.
The people who lived here before us used to rent out the upstairs of the house to people in order to make extra cash.
Apparently one renter was a bit nuts in the head, and they installed dead bolts on almost every door in the place in order to keep the guy out because he would steal things and sell them for money for drugs.
I removed all the interior dead bolts except for this one. We don't have kids, so there is no issue with that. But my wife liked the idea of the dead bolt on the basement door because she was afraid the crazy drug guy might come back someday and try to get into the house.
There is actually a key hidden in the basement to unlock the dead bolt if need be.
Jim