Janis Elsts

Normally when you login to your blog WordPress will create a session cookie that is used to authenticate you. If someone was to steal the cookie they would be able to use it to get full access to your blog without having to know your password. This plugin prevents that from happening – it makes the cookie specific to your IP address, so it won’t be usable from a different computer.
Use this plugin if you have a static IP. If you have a dynamic IP address and it changes often you will get logged out frequently.
A bit more info can be obtained from the <a href="http://w-shadow.com/blog/2008/07/12/safer-cookies-plugin-for-wordpress/" title="Safer Cookies homepage" rel="nofollow ugc">Safer Cookies homepage</a>

Safer Cookies

Ties the WP session cookie to your IP address so that it can't be used to get access to you blog from another computer.

Firdaus Zahari

This plugin allows you to track all user devices used when logging in to your site. The user agent, login date/time, and logout date/time (if the users log out from the site) are tracked automatically and persisted into the database for later viewing.
You can find a list of all login devices available under the Users > Login Devices submenu.

FS Login Devices

Track and display all users devices used during authentication process

Safer Cookies vs FS Login Devices