Police chiefs are warning owners of keyless cars of a spike in thefts by criminals using mobile gadgets to copy their electronic codes.
Between May and June, vehicle crime increased by 3.1%, provisional figures from the National Police Chiefs' Council (NPCC) show – the bulk of it down to keyless theft.
They are using so-called relay technology to receive the key's signal from inside the car owner's home, transfer it to a portable device, and unlock and start the vehicle, says the NPCC.
Assistant Chief Constable Jenny Sims said: "Whilst the rapid development of technology has dramatically improved the experience of drivers it has also allowed criminals to exploit weaknesses in electronic security.
"I would urge drivers to take simple steps to keep their vehicle safe like storing your keys in metal tins or protective pouches that block the devices criminals are using.
"A return to basics like making sure your car is locked is worthwhile too.
"We know from research that some owners think that cars automatically lock – they don't. Always double check before you walk away that it's locked."
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Police say they are working with car makers to share details of gadgets seized from thieves and overcome the technology loopholes.
What is relay technology?
The high-tech method criminals favour was explained by Auto Express in December: "Working in pairs, one thief will stand by the car with the transmitter while a second carries the amplifier around the perimeter of the house.
"If the key is close enough, the amplifier will be able to boost its signal and direct it to the transmitter.
"This transmitter then effectively becomes the key, and tricks the car into thinking the real key is nearby, whereupon the thieves are able to open the car, get in and drive away.
"The whole process can take as little as 60 seconds and can be completed in near silence."
Last week, seven members of an organised crime gang were convicted more than 50 keyless thefts involving vehicles totalling £2.4m in Leicestershire. They were jailed for a total of more than 30 years.
Earlier this month, in Liverpool, five people were sentenced to a total of more than 23 years in prison for a range of crimes including the theft of keyless cars totalling around £2.6m.
And also last week, a man in Cheshire was convicted of several car and key burglaries – and was sentenced to more than seven years in jail.
Jack Cousens, head of roads policy for the AA, said: "Technology sold as a convenience for drivers is becoming the best tool for car thieves.
"Relay theft is now the preferred way to steal a car as it is quick and quiet. The days of 'smash and grab' are over and have been replaced with 'bounce and roll' as thieves now bounce the signal off the keys in the house on to the car and roll away with the goods.
"As fast as manufacturers try to develop ways to strengthen vehicle security, thieves will work just as hard to beat them.
"The best way to protect cars with keyless entry is to keep keys away from the front door and to buy a (security) pouch.
"For less than a tenner, this stops the signal being broadcast and will keep the car where it's parked. Drivers should remember to buy two pouches – one for main key and one for the spare."