How do I ensure only Region Monitoring capable devices can see my app in the store?

Apple's Location Awareness Programming Guide suggest to include the location-services and possibly the gps for UIRequiredDeviceCapabilities.

My app requires the Region Monitoring APIs. How do I ensure only capable devices can see my app 开发者_开发百科in the store?

You're right, location-services and gps will allow devices other than the iPhone 4 to install your app. You could pick some other feature though that you know is iPhone 4 exclusive, like camera-flash or gyroscope and require that one.

I'm not entirely sure whether apple will frown upon a restriction without an apparent need, however gyroscope appears to me like a likely restriction in a navigation enabled app. If you try this approach, I'd explain things in the text field for the comments to the reviewers. Another caveat would be that you'd risk that a future device wouldn't "fit in" - an hypothetical iPhone mini which would feature region monitoring but lacking a gyroscope or camera flash wouldn't be able to install your app, for example.

To be entirely honest, If I were you, I'd ask apple to make sure.

Check out UIRequiredDeviceCapabilities - Apple Developer Documentation. Basically exactly what you said. Are you looking for instructions on how to do that?