The phone sleuths at XDA-Developers have unearthed a handy undocumented feature in the latest version of Android.
Phones running Nougat 7.1.1 are able to invoke a "panic button" by pressing the back key four times. It's in the AOSP source code for the Android Window Manager. Panic mode returns the user to the home screen, meaning that malicious apps which hog the input queue no longer receive focus.
The XDA post explains how it's implemented.
It's a welcome feature, with just two flaws. It's up to the phone OEM to decide whether to implement Panic Mode, and we don't know of any who have as yet. And it needs to provide hooks so the user can terminate the malicious app (with prejudice). Users report that 7.1.2, still in beta, does provide the ability to terminate an app with a long press. But again, it's up to the phone maker to implement the option (killing the foreground app is one of the most widely requested technique on developer forums).
The Nougat 7.1.1 update was officially released in December, and 7.1.2 landed in April. Android O was unveiled in May, the month 2016's Nougat crawled past the 10 per cent figure for user adoption. Around 60 per cent of the installed Android base runs code released in 2014, or before. The O release includes Project Treble, intended to make OTA updates easier to roll out. ®