is it possible location in killed state in watch os app?

This is not possible. CoreLocation APIs that would function after an app has been killed are not supported on watchOS.

In iOS, we can use the method startMonitoringSignificantLocationChanges to fetch the location even when the app is in a killed state, after a significant distance change (for example, 200 meters).

However, this method is not supported in watchOS. Why is that?

Could you please explain this so I can inform my client that it's not possible in watchOS?

While the answer is NO for your specific question about startMonitoringSignificantLocationChanges(), if instead you wanted to use the new CoreLocation APIs, like CLBackgroundActivitySession with CLLocationUpdate and the equivalent of startMonitoringSignificantLocationChanges() CLMonitor

These new APIs will relaunch an app after a crash on watchOS, or if the system terminates the app to free resources. But will not relaunch if the user terminates the app.

These are only available on watchOS 10 and later. If that limitation is acceptable to your use case, then this new APIs will be your solution.

If you would like to learn more about these, you can also watch the WWDC sessions these were introduced at:

• Discover streamlined location updates
• Meet Core Location Monitor
• What’s new in location authorization

The sample projects Adopting live updates in Core Location and Monitoring location changes with Core Location demonstrate the use of these new APIs.