A Lidl car park has been dubbed the "Bermuda Triangle" - because of the mystery over drivers' key fobs that keep breaking.
The bizarre fault has meant dozens of shoppers have been unable to unlock or lock their vehicles.
Others have been unable to disable their car alarms in Kingswood, Gloucestershire.
One resident said: "It's like the Bermuda Triangle."
Locals believe the problem has been caused by Internet-based traffic cameras in the car park which are blocking signals.
Graeme Wakerley, 65, said: "It's bizarre. I assumed the batteries were flat as you would in that situation.
"My son brought a spare and that didn't work either."
The retired policeman found his key fob wasn't working when he returned to his car.
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But it also happened the other way round, when a customer has arrived at Lidl and been unable to lock their car.
And a pregnant mum, who visited the store with her toddler, said: "I had to get in the driver side with him on me to try to start the ignition to then use the lock on the dash to unlock the other doors to get him in the car.
"It's hardly a safe experience."
People on a Facebook residents group shared their fury.
One woman wrote: "Glad it's not just me! Myself and a lady next to me looked at each baffled yesterday literally had to stand right next to the front of car.
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"It's been happening a while and when I had hubby's car thought battery dead."
Another person said: "That happened to me the other day and I bought new batteries only for it to work when i got home."
Lidl said the cameras do not transmit a signal which could block a fob and revealed the supermarket chain does not know what is causing the fault.
A spokesman said: "We were concerned to learn of this occurrence, and are currently looking into the matter to help identify the cause, and resolve the situation for our customers."
