Gmail offers 2-step verification to secure your account. This is an optional feature but is a good step towards securing your email account.
This can be activated by going to the 2-step verification page under your account. You can follow the link below.
Once you activate this, signing in will require your user name, password and in addition a 6-digit code. You can get this code on your cell phone via sms or using Google Authenticator.
Installing Google Authenticator on your smart phone (Android,iPhone,iPad,Blackberry).
Here is a useful link:
When you want to authorize your gmail account on non-browser devices, mobile application or desktop application which do not have an option to accept the verification code, You need to generate application-specific passwords for each. This can only be done after you have 2-step verification turned on and is only needed to be done once. Do not need to remember this password once you have entered it. You can follow the link below to generate application specific passwords in your account.
If you lose the device which you activated using the application specific passwords. You can simply revoke access to that device.
If you lose the device that was authorized with an application-specific password, you can revoke its application-specific password so no one can access your Google Account from that device.
Here are some links explaining google 2-step verification in detail: