A sensor is a module that is sensitive to changes in its environment and sends information to a device about those changes.
Devices collect sensor data and forward it to the cloud. Devices can be quite small, and have very few computing, storage, and so on resources. They could only communicate via networks that can not directly access a cloud server, such as over Bluetooth Low Energy (BLE). Conventional devices are more likely to look like small machines, and may be able to store, process, and analyze data before it is sent to the cloud.