Do smart door and window sensors require a hub?

Most of the highest-rated options do. Across the reviewers we read, sensors from Aqara, Eufy, Philips Hue, and Tapo all require their respective hubs/bridges, which is what enables the long battery life and reliable low-latency notifications. True Wi-Fi sensors exist (ecobee's SmartSensor, various Tuya-based kits), but specialist communities consistently note they trade battery life and snappy response for hub-free convenience.