What happens if a Tamagotchi doesn't turn the lights off?

Not turning the lights off after a Tamagotchi has gone to bed will result in a care mistake as well (though on certain releases the attention icon will remain on for an hour before a care mistake occurs), except on releases (such as the color Tamagotchis) where the light icon is absent.

What happens if a Tamagotchi meter is empty?

When one or more meters are empty, the Tamagotchi will inform the user by beeping and highlighting the "Attention" icon. If fifteen minutes have elapsed and the user has not tended to the Tamagotchi's needs, the attention icon will turn off resulting in a care mistake.

What is a Tamagotchi meter?

It is a measure of how many times the user has forgotten to care for their Tamagotchi, which factors into what character it will evolve into or how close it is to Death. When one or more meters are empty, the Tamagotchi will inform the user by beeping and highlighting the "Attention" icon.