It is possible to detect if my framework is running as part of the main app or an extension?

In an iOS or OS X Framework, which contains common code for both it's App, and app Extensions, is there a way to detect if the code is being run under the main app, or one of it's extensions? Specifically I'd like to detect if the framework is being used as part of a WatchKit extension as opposed to within the iPhone part of the App.

UIDevice.currentDevice always returns the iPhone as that is what is running the code. I believe I could check if WKInterfaceDevice exists, but that doesn't seem too elegant.