Two men forced their way into a Macarthur Crescent home in Bitterne, assaulted a man and made off with cash and a phone in what police think was a case of mistaken identity.
It happened between 9.30pm and 9.40pm on Saturday, November 7.
Police say two men knocked on the victim's door before forcing entry and committing the offences The pair then forced entry to an adjoining property, where it's believed nothing was stolen.
A third man was also seen entering this address.
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Although the victim didn't need hospital treatment, he'd been left very scared and shaken by what had happened to him, said Detective Constable Dal Andrews.
DC Andrews added that police thought it was a case of mistaken identity, with the offenders going to the wrong address. He reminded residents to be vigilant and not to answer the door to anyone asking to enter on the pretext of looking for another person.
Anyone with information can contact the police by phoning 101, or call the Crimestoppers charity anonymously on 0800 555 111.