Television with a caution alarm
It is normally seen in many households (at least in my household) that older people (sometimes we youngsters) tend to go asleep while watching television. So we can have a television set which gives a message, every 1 hour or 40 minutes, indicating that the television set is ON. Mind you! This message has to be a voice message, which can be easily installed in a television set.
Example of a voice message: "Your television set is on!" if possible indicating the time.