How theft-proof is the security camera? Can a thief do anything with it after stealing it?

If the camera is stolen, the thief cannot use it. The camera is linked (via the cloud) to the person who added it to the Smartlife app.
If someone resets the camera and tries to add it to a new Smartlife account, a message will appear saying the device is already linked and must first be unlinked by the original owner.
A thief can contact us and request to disconnect the device, but in that case, we will have their contact details and can take further steps to return the camera to the rightful owner, if needed.