I have a program that works with two devices (phone and laptop). On each device you can sign up and log in unless you have already done so. Once the user has either signed up or logged in on either device they cannot reach the log in/sign up page again and they just reach what they really want on start up.

The problem with this, is that if the user, for example; First signs up on the mobile device. And then following that, signs up on the laptop (instead of logging in) they will be permanently stuck without the two programs working in conjunction... Unless the client re-downloads either program (never what one wants)

What should I do to prevent this from happening?

  • The user will be registered in the database when he first signs up. So, it should show "User already registered" when he tries to sign up with the same email/username on website. I guess there should be no issue here unless the database is not persistent. 9
    – Adit Gupta
    Aug 26, 2015 at 19:38
  • I am saying if the user decides to create a whole new account though!
    – maxisme
    Aug 26, 2015 at 19:58
  • 2
    You can take a hint from Stack Exchange. They have a process for it - stackoverflow.com/help/merging-accounts
    – Adit Gupta
    Aug 26, 2015 at 20:03
  • so, once a user logs in, they can literally never sign out?
    – AlannaRose
    Aug 26, 2015 at 23:22
  • Correct. . . . .
    – maxisme
    Aug 27, 2015 at 6:56

1 Answer 1


First off, your users have a non-zero responsibility to learn how computers work. You can help them by designing something that is easy to use, etc. but it is not your job to prevent all possible user error. This is an example of that. You can help the problem, but you won't be able to stop it.

Some methods to ease the issue:

  • You should allow merging of duplicate accounts
  • If you have a primary device, consider making signup only possible from that device, and login only accessible from the secondary device (eg. Instagram does this on their app vs website)
  • You can use a login method for which people are unlikely to have multiple variants of (eg. Facebook, phone number, SSN, etc)
  • Send a welcome email when people signup. This makes it easier for people to look through their email to see if they have already signed up.

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