http://www.epvelectronics.com/en/occupancy_sensors_presence_detectors.html Occupancy sensors (also called presence detectors) are a great way to improve a building's energy efficiency and to save money. Occupancy sensors are very sensitive motion sensors that are designed for demanding application (such as offices) where they need to detect very fine motions - a task that conventional motion sensors usually do not master. EPV occupancy sensors offer market leading sensitivity due to their digital sensor head technology which offers excellent sensitivity and at the same time makes them immune to false triggerings. These occupancy sensors are available in a wide range of models in order to fully cover all your project requirements.
Their small size offers a very elegant and unobtrusive integration into the ceiling.