In the Netherlands we have the sireneradar.com initiative. Most emergency services are connected to this system.

The location of the police/fire/ambulance-vehicle is reported realtime to the platform, That data is available to navigation vendors like TomTom and Flitsmeister, and they sound and display a warning to their users for an approaching emergency vehicle.

This way the Waze users get an early warning, so they can be extra alert when they need to.