The Siemens PMI-3 is a significant upgrade over the PMI-2, offering enhanced functionality and improved performance. Some key features of the PMI-3 include upgraded sensor technology for more accurate detection, expanded communication capabilities for seamless integration with building management systems, and advanced diagnostic capabilities for easier maintenance and troubleshooting. Overall, the PMI-3 represents the latest advancements in fire alarm technology, providing enhanced safety and reliability for modern buildings.