Good day MIT app inventor, it's a huge honour of sharing my gratitude of thanks to you for a wonderful app inventor you have come out with. I am Mopelola Emmanuella Adegoke a delegate student of Sonmori Senior Comprehensive High school, and I do not know how MIT inventor can make an app that detect unauthorized access to any transactions done on the mobile phone and notify the user too.
Please MIT app inventor, I would be so grateful if I can be enlightened on how that kind of app can be created using MIT app inventor
This is probably not possible, at least using the native Blocks. How do you define an unauthorized access? You can design an app that requires passwords and that would limit who can access the app you design to do 'transactions'. Unfortunately someone could guess a password so you cannot make a totally secure app. 
You could also use a database that has its own authorization security (firebase or google sheets used as a database).