More than a dozen motorists were left stuck in a car park when a car's central locking system malfunctioned and blocked drivers' key fobs.
Some motorists tried replacing their batteries
Some cars failed to start on Tuesday in Parrock Street car park, in Gravesend, Kent, while others would not unlock.
Stranded drivers were left to call motoring organisations for help.
However Gravesend Borough Council had been investigating similar problems in the car park for weeks. Finally Ofcom was called and the offending car found.
A spokesman said "weeks of sleuthing" by council officers had them looking for a rogue transmitter or wireless broadband unit in nearby offices.
Staff also checked all transmissions in and around the car park, because of nearby communications at the town's Civic Centre and police station.
A recently-installed system transmitting car park usage each minute to display signs across Gravesend was also checked.
"All the time the situation seemed to be worsening with the last straw this week when more than a dozen motorists were stuck," he added.
He said alarms had been going off, and drivers had experienced "mysterious and sporadic" difficulties with car locks.
Some people tried replacing their fob batteries, he added.
Ofcom was finally called and a survey found a small family car was intermittently sending out signals blocking other fobs in a 164ft (50 m) radius.
A notice was placed on the car informing the owner - a commuter who left his vehicle there all day.
The spokesman said: "The driver was unaware of the problems his car had been causing and has now made contact with us and the problem will be fixed once and for all."