Trial app

Take a look at THIS tutorial.

Thanks NJDude.

However - I failed to mention it in the first post - my app will be used a lot in areas where there are no cell or internet connection. Some users may be in such areas for weeks at a time. The system must not depend on internet connection.

All controls must be on the device itself.

It's possible by storing the info locally, however the trial could be easily bypassed by clearing the apps cache

I'm thinking of the following:

When the program starts, it checks for a specific file (with the installation date as text) in the "DirInternal" folder. If the file is not found there (the first time the program runs after installation) it will create the file and put the current date in it.
The next (and future) times the program starts, it will find the file and compare the install date (in the file) with the current date, and determine how many days of the trial is left, and if < 0, quits the program after a message.

What's the caveats with such a system - or is there a better (more secure way) to do this without the web?

Make it create a "secret" file somewhere on the SDcard that is hard to find.
That way it doesn't matter if the app is uninstalled and then reinstalled..