By default, only 5 devices can login as the same user on Salesforce1. If you login on a 6th mobile device concurrently, you will be prompted with a message indicating that ‘already 5 login sessions exist.’
At that point, the ‘oldest’ Salesforce1 session will be logged out.
Check the below link form more information
https://help.salesforce.com/apex/HTViewSolution?id=000229663&%3Blanguage=ja
