  In contemporary society, the pressing challenge of preserving user privacy
clashes with the imperative for smart buildings to efficiently manage their
resources, particularly in the context of occupancy monitoring for optimized
energy utilization. This paper delves into the application of millimiter wave
(mmWave) frequency modulated continuous wave (FMCW) radar technology for
occupancy monitoring. mmWave FMCW radar, unlike conventional methods that often
require the use of identifiable tags or involve image analysis, operates
without the need for such identifiers, mitigating privacy concerns. However,
challenges arise when attempting to cover extensive indoor spaces due to the
limited range of individual mmWave FMCW radar devices. The present work
proposes the use of a flexible software architecture to integrate the
measurements of several mmWave FMCW radar devices, so that the whole behaves as
a single sensor. To validate the proposal, an example of use in a real
environment in an indoor space monitored with three mmWave FMCW radar devices
is also presented. The example details the whole process, from the physical
installation of the devices to the use of the different software modules that
allow the integration of the data into a common internet of things (IoT)
management platform such as Home Assistant. All the elements, from the
measurements captured during the test to the different software
implementations, are shared publicly with the scientific community.
