HOW TO KNOW IF SOMEONE ELSE IS USING YOUR FACEBOOK ACCOUNT

Are you Noticing anything Suspicious on your Facebook Account, either through your Wall? Well there are Some Simple Security Settings built into Facebook, Some of these Settings are New and others have been around for sometime.
This Settings Should help you detect if any other person is secretly logging into and using your Facebook Account.

FOLLOW THIS STEPS
Visit Facebook.com => Account => Account Settings => Account Security.
Here you will see a list of all Computers and Mobile Devices that have logged into your Facebook Account and the Time of Visit.

You can also see the Approximate Geographic Location of the Device, based on the IP Address, that was used to Access your Facebook Account.

If you come across an Unknown device / location in the List e.g Maybe you See Mac Computer and you've never used Mac Computer before, Just click on the Corresponding "End Activity" link and it should immediately log out that person using your Account.

NOTE:
For Extra Safety, You may also choose to to Receive email and SMS alerts if someone else tries to log into your Facebook Account from a Previously Unknown Computer or Mobile Phone.

Goodluck!!!