on facebook when 2 people are logged in the same account?

[CREAM]

and one turns off chat will the other person know it

[Pankaj]

when that people use the facebook in two mobiles or computers.

[Arvind]

No. If you turn off chat the other peson will not be able to know whether you are online or not.

[zaheer]

There is security system in facebook which tells users when they are even logged on from, a different computer than the usual one.
If the user has optimized the security level he ll get to know as soon as someone signs in from a different user.
The facility also shows the place from where it has been logged in , in form of map.

[mickie]

Other person did 't know about it. But after some time that account will become suspicious and may be suspended.

[Fauzi]

If two people logged in the same account if any of them make change to the account I think the other person would notice the change. for example that chat, if one person turn off chat, another person who logged on the same account would notice it when that person is about to chat.