We are using different Internet of Things devices (access systems, motion detectors etc.) which report to one system. This system transfers the data to an SQL Server 2012 (or higher)installed on a Windows Server. In this scenario, how do we have to license the SQL Server?

The Internet of Things-devices (IoT-Devices) do not directly access the server nor the database. However, the IoT-Devices are indirectly communicating with the server via a third-party sytem. In Microsoft terms, this is referred to as Multiplexing.

However, Multiplexing does not reduce the amount of required licenses.

There are two ways to license the accesses on the SQL server: the Server+CAL licensing model and the per Core licensing. In this case, the Server+CAL model does not make much sense since you would be required to cover any IoT-Device with a CAL.

The benefit of using the per Core licensing model is that it covers an unlimited number of users/devices which could access the server. Therefore, the per Core licensing model is recommend for this scenario.

Sources:

Microsoft Product Terms_March 2017 Microsoft SQL Server 2016 Licensing Guide_as is 2016-08-28