Dual Technology Sensors
In 2017 ETC released a White Paper on Dual Technology Sensors by Bryan Palmer that is still pertinent today.
Introduction
Dual technology occupancy and vacancy sensors have become standard specification items for most architectural and commercial projects. While most sensors that implemented a secondary technology were similar early on, there are now multiple technologies used, which offer advantages and disadvantages depending on their use and implementation. This document identifies the common technologies used and where they work best.