# Make mobile numbers unique - prevent users with same mobile to sign up again **URL:** \ **Category:** Get Help\ **Created:** [February 11, 2020, 8:32pm UTC](https://community.auth0.com/t/make-mobile-numbers-unique-prevent-users-with-same-mobile-to-sign-up-again/37756 "2020-02-11T20:32:23Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![weseba](https://sea1.discourse-cdn.com/auth0/user_avatar/community.auth0.com/weseba/32/12977_2.png) [@weseba](https://community.auth0.com/u/weseba)\ **Post date:** [February 11, 2020, 8:32pm UTC](https://community.auth0.com/t/make-mobile-numbers-unique-prevent-users-with-same-mobile-to-sign-up-again/37756/1 "2020-02-11T20:32:23Z")
Hi all, I would like to make users unique based on their mobile number. This should prevent creating fake accounts in my application. Can I do this within Auth0 Hooks / Rules? ---
**Author:** ![jmangelo](https://sea1.discourse-cdn.com/auth0/user_avatar/community.auth0.com/jmangelo/32/7923_2.png) [@jmangelo](https://community.auth0.com/u/jmangelo)\ **Post date:** [February 12, 2020, 3:52pm UTC](https://community.auth0.com/t/make-mobile-numbers-unique-prevent-users-with-same-mobile-to-sign-up-again/37756/2 "2020-02-12T15:52:34Z")
Technically if you only allow users to login through a passwordless SMS connection ([Passwordless Authentication with SMS](https://auth0.com/docs/connections/passwordless/guides/sms-otp)) you have achieved your requirement implicitly. If you need to allow other means of login, you could still technically use this connection and account linking to ensure each user has a verified mobile number. ---
**Author:** ![weseba](https://sea1.discourse-cdn.com/auth0/user_avatar/community.auth0.com/weseba/32/12977_2.png) [@weseba](https://community.auth0.com/u/weseba)\ **Post date:** [February 15, 2020, 10:40am UTC](https://community.auth0.com/t/make-mobile-numbers-unique-prevent-users-with-same-mobile-to-sign-up-again/37756/3 "2020-02-15T10:40:36Z")
I need both. E-Mail and Mobile. How does this account linking work? Can this give the user an error if he tries to sign up a second time with same mobile but different email? ---
**Author:** ![jmangelo](https://sea1.discourse-cdn.com/auth0/user_avatar/community.auth0.com/jmangelo/32/7923_2.png) [@jmangelo](https://community.auth0.com/u/jmangelo)\ **Post date:** [February 17, 2020, 3:05pm UTC](https://community.auth0.com/t/make-mobile-numbers-unique-prevent-users-with-same-mobile-to-sign-up-again/37756/4 "2020-02-17T15:05:48Z")
There’s reference information on account linking at ([https://auth0.com/docs/link-accounts](https://auth0.com/docs/link-accounts)). Although it would require custom logic on your side to ensure each account has an associated SMS passwordless account it is technically feasible for you to perform a custom integration where a user after signing up with email are forced to also a mobile number (SMS account). ---
**Author:** ![weseba](https://sea1.discourse-cdn.com/auth0/user_avatar/community.auth0.com/weseba/32/12977_2.png) [@weseba](https://community.auth0.com/u/weseba)\ **Post date:** [April 4, 2020, 11:37am UTC](https://community.auth0.com/t/make-mobile-numbers-unique-prevent-users-with-same-mobile-to-sign-up-again/37756/5 "2020-04-04T11:37:40Z")
I ended up implementing my own solution. That hast the benefit that I can let the user login with his email and later ask him for his mobile number. I might link it to auth0 later. ---
**Author:** ![konrad.sopala](https://sea1.discourse-cdn.com/auth0/user_avatar/community.auth0.com/konrad.sopala/32/13516_2.png) [@konrad.sopala](https://community.auth0.com/u/konrad.sopala)\ **Post date:** [April 6, 2020, 9:04am UTC](https://community.auth0.com/t/make-mobile-numbers-unique-prevent-users-with-same-mobile-to-sign-up-again/37756/6 "2020-04-06T09:04:16Z")
Thanks for letting us know!