I live alone, but I start most mornings making a cup of tea. This daily ritual was passed on to some of my family members, so this can be used by them, as well. Often by the time I get to my tea, it is uncomfortably cold, having steeped while I worked through other parts of my morning routine.
The device will show the temperature range of the tea. Red, too hot. Blue, too cold. Green is just right. Additionally, it will an SMS when the tea is ready.