18. Lookout Mobile Security
Cost: Free for the basic version; the premium version ($2.99 month or $29.99/year) adds safe browsing features, privacy protection and the ability to backup photos and your call history.
Available on iOS too? Yes
This app protects your smartphone against viruses and other types of malware. The app backs up your contacts, helps you remotely locate your device if you misplace it or if it was stolen. If your phone was stolen, you’ll want to upgrade to the premium version, which lets you lock and wipe your phone and even set off a “scream” alarm, which should be loud and intrusive enough to convince thieves to set down your phone and walk away.