You can have your iPhone's LED light flash whenever a notification comes
in as an extra way of alerting you to new activity: from Settings,
choose General then Accessibility and then toggle LED Flash for Alerts
to the on position.
On Android Marshmallow, go to Settings, Security and Screen pinning -
when activated, you can 'pin' apps from the multitasking screen, so the
app can't be left without a PIN. Handy for lending your device to others