If you were paying attention earlier, you probably already know the answer to this question. But, if you are glancing around through this guide, it is important that you understand this. If the sensor you are buying does not require a hub, it will probably work with or without Wi-Fi. Of course, you will not get the benefits of Wi-Fi such as alerts from your smartphone. As for an external hub, this will need to be present as this will be an essential piece of communication.