Ask HN: What is the killer 'internet of things' app?

We keep hearing about how big the Internet of Things is going to be - but I find it difficult to see practical apps that would be extremely important in everyone's lives (e.g. google maps on phones is an important mobile app today).

What is the true potential of IoT beyond phone-controlled washing machines, refrigerators? I would love to get some perspective and understand from YOU - what do you think can be the 'game-changer' or 'killer app' for internet of things. Thanks for sharing your thoughts.