Unlock Key Component

I have almost completed my Android application so am considering ways of distributing the application. I have seen some applications on Market have free limited/locked version and separate Unlock Key/License Key which unlocks extra functionality.

How is this done? Has anyone here done this? If so, how well does it work?

I am th开发者_StackOverflow中文版inking maybe this is better then having two versions of the same application (i.e Lite and Pro).

Thanks.

Done some more research and I found post by author of AppSwipe on how they solved this problem. The idea is to have static method that returns boolean value indicating whether the end user has key component installed or not. The check is done using PackageManager signature check.

More details