Ofcom engineers are investigating how a faulty Freeview set-top box could have triggered an RAF air-sea rescue mission.
The set-top box in Portsmouth apparently generated a Mayday signal identical to that used by emergency beacons, and was picked up on January 5 by satellite and forwarded to RAF Kinloss in Scotland.
From there coastguards on the south English coast were alerted and a helicopter scrambled.
After a two-hour sea search off Portsmouth it was established that the signal was coming from the mainland. RAF chiefs called Ofcom and the communications regulator quickly determined the signal was coming from a home.
Ofcom engineers removed the faulty Freeview box and are now examining it.