So I didn't want my mom going through my laptop, so I put a touch screen on it where you just have to tap the screen to unlock it. Jokes on her, she doesn't have any fingers.
Touch Screen Security
Explanation
The joke plays on the expectation that a touch screen would be a convenient security measure, but it turns out to be an impossible hurdle for the person's mom, who has no fingers. It's a dark and morbid type of humor because of the physical disability of the mother.