The architectural pattern used for the realization of the majority of the IoT use cases follows the event-driven architecture pattern. The event-driven architecture software pattern deals with the creation, consumption, and identification of events. An event can be generalized to refer the change in state of an entity.

For example, a printer device connected to the internet may emit an event when the printer cartridge is low on ink so that the user can order a new cartridge. The following diagram shows the same with different devices connected to the internet:

 

The common capability required for devices connected to the internet is the ability to send and receive event data. This can be easily accomplished with RESTful APIs. The following are some of the IoT APIs available on the market:

• Hayo API: The Hayo API is used by developers to build virtual remote controls for the IoT devices in a home. The API senses and transmits events between virtual remote controls and devices, making it easier for users to achieve desired actions on applications by simply manipulating a virtual remote control. 
• Mozilla Battery Status API: The Mozilla Battery Status API is used to monitor system battery levels of mobile devices and streams notification events for changes in the battery levels and charging progress. Its integration allows users to retrieve real-time updates of device battery levels and status.
• Caret API: The Caret API allows status sharing across devices. The status can be customized as well.