Application that works for iPhone and Android devices. When in locked screen, can do an action (e.g. double-tap power button) which enters your phone into 'GoodSave mode'. This changes the required password to enter phone and even if get password correct, disables or hides various apps. This GoodSave mode is enabled for a pre-selected period of time and can only have it active one at a time (i.e. need to wait for time to expire or to successfully login and disable in the app).
Application must be very low cost to battery (available everytime lock screen) and discrete (so anyone looking at phone does not know it is in GoodSave mode).