Android Protector is a free program which protects any Android application with a password/pin code. Just install it onto your Android smartphone and it will automatically lock down your Gmail, calendar, contacts and other apps containing sensitive data. It’s a little hit or miss in the current version, I found that the direct Gmail icon bypassed the security completely, but it’s a decent enough start. Free version protects up to 10 apps, the commercial version offers unlimited protection.
Protector runs as a background service consuming negligible amount of memory and passively waits for start of protected applications. Once user clicks an icon to start such application, full-screen window is shown on top, asking for a password. If user clicks Cancel or anyhow closes the window, protected application is immediately sent to background to make sure that it can’t be used without a password.