Hi Shrishti,

For the CAT examination, The list of prohibited thing is as follows:

Electronic gadgets including phones, watches, cameras, bluetooth devices etc.

Jewelry with metal in them.

Cholthing items with pockets.

Although it is not categorically mentioned, it is probably not a very good idea to carry metal keys inside the examination hall as the penalty for being caught with prohibited items inside the examination hall is direct disqualification. However, the center will not take responsibility for any item which is kept outside the examination hall. It is advised to take public transport or ask someone to drop you and pick you up  again.