Many smart devices will piggyback on the same network you already use in your household. For example, your smart television might simply connect to your Wi-Fi network to stream content and update its firmware and apps.
Other devices can use their own, sometimes proprietary, networks. These are often called mesh networks, and they usually consist of a hub that connects to Wi-Fi and a low-power radio wave network connecting every other device to each other.
Some devices – especially those designed to be mobile, like fitness trackers and medical devices – will use mobile internet to connect to a cloud service. These will typically also connect to a local device like your phone using Bluetooth.
Larger business environments might instead have smart devices that use a low-power wide area network (LPWAN). This sort of network can spread for kilometres, so it’s particularly useful in industrial settings.