Piezo harvesting switches and similar (I think there’s a flywheel design out there too) are quite expensive, not terribly reliable or consistent, and require substantial activation force. Conventional switches and batteries that can last for years in remote push buttons and sensors are extremely inexpensive in volume.

> for detecting other events like doors opening/closing etc.

If any of those doors are important for security, then I'd want something an intruder can't easily jam or spoof.