Spectrum mystery leaves baffled shoppers stuck in car park

01 March 2021

Picture the scene – you’ve braved the supermarket and have a full trolley of groceries to pack in the car and get home.

But there’s a problem. You can’t unlock your car. For some reason the key fob isn’t working. And looking around, you can see lots of fellow shoppers in the car park having the same trouble.

This is what happened a few days ago at a Tesco car park in Royston, Hertfordshire. Many shoppers at the superstore were having difficulties locking and unlocking their vehicles. These issues then led to other problems, including car alarms inadvertently sounding and resulting in a number of callouts to vehicle recovery services.

While one member of the public likened the mystery to ‘some sort of alien phenomena’, the explanation was likely to lay a little closer to home.

What's this got to do with Ofcom?

Car key fobs, like lots of other everyday technology, use radio spectrum to operate. On rare occasions, faulty or unauthorised equipment can interfere with nearby technology and prevent it from working properly – such as in the case of these customers’ fobs.

Ofcom’s Spectrum Management Centre, based in Baldock, Hertfordshire, provides a 24-hour service to industry and to members of the public, by monitoring the radio spectrum. This service also allows people to report radio interference.

On Friday 26 February, an officer from Hertfordshire Police contacted us to make us aware of the problems at the supermarket car park.

Due to the nature and scale of the problem, we assigned this as a high priority case, and sent out a local engineer who was soon on the scene to investigate the problem.

Within 30 minutes, our spectrum engineer arrived at the car park to investigate the problem. To do this, we use a spectrum analyser – a piece of equipment which measures the airwaves and detects any radio signal which shouldn’t be there. However, at that particular moment the problem wasn’t actually happening, and customers were able to lock and unlock their vehicles successfully. So, we asked staff at the supermarket to get in touch if any more customers reported further issues over the weekend.

Subsequently, we received a further call on Sunday 28 February telling us that another customer could not get into their car. The same Ofcom engineer made another visit, however, once again the problem wasn’t taking place. On further investigation it appears this issue was an unrelated fault with the customer’s car rather than a wide-spread interference issue.

It’s difficult to say what might have caused these particular issues at this location, but it is likely to have been something fairly innocuous and accidental. Previous similar cases we’ve investigated found the culprits to be a faulty doorbell, and some retro lightbulbs. So, shoppers can rest assured that it was unlikely to be anything sinister behind the problem – and certainly not alien phenomena!

We’ve advised the supermarket to keep an eye on this situation as it could potentially return, and if it does, they should get back in contact with us as soon as possible so we can carry out a further investigation if needed.

For now, as it stands, customers will be relieved to know they’re able to get into their cars without any problems.

What is spectrum?

You can’t see or feel radio spectrum. But any device that communicates wirelessly needs spectrum – such as televisions, car key fobs, baby monitors, wireless microphones and satellites. Mobile phones use spectrum to connect to a local mast so people can make calls and access the internet.

Why does Ofcom manage spectrum use?

Only a limited amount of spectrum is available, so it needs to be managed carefully. Certain bands of spectrum are also used for different purposes. For example, mobile companies use different parts of the spectrum to TV companies. So, it needs to be managed to prevent services interfering and causing disruption to people and businesses.