Use Devise for two different application in separate machines

hi,

I am trying to have my devise database be used by two or more separate rails application.

 I have pointed my sub-application to use the main application devise database.
however, when i log in via my main application and then my sub-application.
the sub-application don't seem to automatically log in.

is this because devise is storing the session as cookies and hence the sub-application does not have access to the cookies?. if so, is it advisable to switch all my application to have their session stored in the database instead?