One of the key parts of mobile security is preventing unauthorized people from being able to use your smartphone if they get hold of it, whether it’s for the minute or two that you’ve stepped away from the table, or for an hour or more after it’s been found or stolen.
The first and easiest solution: Use a screen lock to require authentication.
Authentication and time-lock security features are baked into all current mobile operating systems — they are typically found in Settings; enabling them doesn’t take more than a minute or two.
There are a variety of options, depending on your operating system. My iPhone 4 running iOS 7, for example, only supports a simple four-digit numerical passcode or what it calls a “non-Simple” passcode, which can have more alphanumeric characters — harder to guess, but also harder to keep re-entering whenever the lock screen appears.