Police and ambulance staff were called to a house in Firhill, Alness, after Nickolas Bowes, 18, collapsed.
Efforts to revive him on the way to hospital in Inverness failed.
Police have declined to comment on a report that Mr Bowes stabbed himself by accident trying to remove a tagging device.
Detective Inspector Vince McLaughlin, who is leading the investigation, said: “This death is still being treated as unexplained and it would be inappropriate for us to comment further on the circumstances until these inquiries are complete.”
The Scottish Police Services Authority yesterday carried out an examination of the house and a post-mortem examination is due to be made today.
Chief Inspector Gus MacPherson, Northern Constabulary’s area commander for Ross and Cromarty, said: “This is a tragic death, the full circumstances of which are still being investigated.”
He said police were not looking to trace anyone else in connection with the death.
Mr Bowes’ sister, Emma, and his stepfather, Trevor MacPhee, issued a statement saying: “We are all devastated and numb at the loss of our happy and lovable Nick, who cared deeply for his family.
“We would like to thank all our neighbours and friends who are supporting us through this sad time.”
Local councillor Caroline Wilson said Mr Bowes had been wearing a tag, which was due to be removed next week, but reports about his death were “speculation”.