Are you interested in receiving beta versions of the app which contain new features and/or bug fixes (and possibly new bugs) which aren't yet available through app store yet?
If you want to receive beta versions of Scanner Radio, go to https://play.google.com/apps/testing/com.scannerradio and follow the instructions on that page.
If you want to receive beta versions of Scanner Radio Pro, go to https://play.google.com/apps/testing/com.scannerradio_pro and follow the instructions on that page (you can only receive beta versions of Scanner Radio Pro if you've purchased the app).
You can leave one or both beta programs at any time by going to one of the links above and clicking on the "Leave the program" link.
If you want to receive beta versions of Scanner Radio for iOS, install Apple's TestFlight app, then go to https://testflight.apple.com/join/uKCjxQNM on your iPhone or iPad to become a beta tester of the app, then tap on "Start Testing", and then tap on the "Install" button to install the latest version of the app.