We have a photocell-triggered LED nightlight plugged into the wall outlet in our hallway. After we first plugged it in the cat came over to check it out and I showed her that if I covered the photocell with my finger that the light would come on.
I doubted that she'd make the connection but as a typical cat she's usually curious about new things in her world. Within seconds she started putting her paw on the photocell and making the light go on and off. She soon got bored of it though. This one might be more to her liking.