A team investigating people being locked out of their vehicles when key fobs stopped working in a car park has found no evidence of interference.
Police received about 100 reports of key fob failure in three days from people using the Tesco car park in Royston, Hertfordshire.
Communications watchdog Ofcom said its spectrum assurance team had checked the site for "signs of interference".
None were found and their investigation had concluded, a spokesman said.
Devices that can communicate wirelessly using radio waves, such as televisions, car key fobs, baby monitors, mobile phones and satellites all make use of specific areas of the radio spectrum.
Interference in this spectrum could affect the technology used to secure vehicles.
Concerns have been raised in the past about weaknesses in keyless entry system technology, including a risk of vehicle theft.
Some worries focused on radio jamming devices blocking signals for remote central locking.
Hertfordshire Police said people had been having trouble locking or unlocking their cars and alarms had been going off, but no cars had been reported as stolen and the issue "was not being treated as [one of] malicious intent".
Tesco said it had been supporting the investigation.