App Lock locks your applications with a pass code to prevent intruders.
Android Device Manager is a built-in anti-theft service found on most Google-enabled Android devices. You access it via a website. You’ll want to enable this app.
Ghostery Browser lets you block website trackers if need be.
DuckDuckGo Search is popular with the security and privacy crowd. It doesn’t track your searches like others, so your habits are private and won’t be tracked.
NoRoot Firewall helps you manage your outgoing Internet connections. Not as powerful as a root-enabled firewall, but worth a look.
For text and calls, Signal Private Messenger may be the best solution. It encrypts your phone to the point where you’re the only one who can see texts or hear the caller.
Sync is good for encrypting and storing files from one device to another.
The Tor Project is an obvious choice for security and privacy. It works better on your computer than it will on your phone, but worth a look
Finally, TunnelBear VPN is a good virtual private network start for beginners and novices.