what kind of 'security' do you have in mind?
security (aka antivirus, anti-malware, anti-exploit)
- typical antivirus/malware is useless (they fail to detect a lot of apps with malware)
- some apps are useful against known exploits (eg: blocks MMS messages vulnerable to stagefright)
- stick with downloading only from official market and from legitimate/mainstream developers
http://arstechnica.com/security/201...elopers-threaten-the-entire-android-userbase/
Of the four AV products tested, only the one from Trend Micro detected any of the exploits, and in that case it was only 13 of the 167 exploits and then only those in the naked, unpacked form.
"security" - aka physical security, against lost/stolen phones (remote wipe or remote-retrieve-gps-location)
- Cerberus, Android Device Manager
"""security""" - aka hide apps/stuff from anyone using your phone (you mentioned "Applock")
- Android has app-pinning - users can only use the current pinned app
- Some gallery/photo managers whitelist certain photos, someone scrolling your gallery can only see certain photos
- "hide" certain apps *cough* tinder
privacy
- disallow apps from accessing your location/phone number/IMEI/email etc
- LEO Privacy guard, Xprivacy, AppOps... usually requires root. Android Marshmallow has some of these features