Hi  @GaryPang 

There is no limit to the number of logins you can have on different devices using the admin account.

But each camera supports up to 2 simultaneous video streams. You could use up to 2 devices to live view the camera at the same time using the Tapo App or the RTSP. You could view the playback on only one device using the Tapo App at the same time. 

You can find the information on this FAQ, Q3.3. General Questions about the Tapo Camera