Hundreds of popular cars - including four of the five best-selling models in the UK - are susceptible to "keyless theft", new research claims.
Consumer group Which? found the Ford Fiesta, Volkswagen Golf, Nissan Qashqai and Ford Focus were all at risk.
Thieves are increasingly thought to be using technology to bypass entry systems on keyless cars.
But industry body the Society of Motor Manufacturers & Traders (SMMT) said "new cars are more secure than ever".
Which? analysed data on keyless - or "relay" - attacks from the General German Automobile Club (ADAC), a roadside recovery organisation.
ADAC tested 237 keyless cars and found that all but three were susceptible.
The latest models of the Discovery and Range Rover, and the 2018 Jaguar i-Pace, all made by Jaguar Land Rover, were found to be secure.
Of the top-selling cars in the UK, only the Vauxhall Corsa was deemed safe because it is not available with keyless entry and ignition.
"Thieves have been using keyless theft for several years, but manufacturers continue to make new models that can be stolen in this way, meaning there is an ever-larger pool of vehicles for thieves to target," Which? said in a statement.
Harry Rose, editor of Which? Magazine, said manufacturers needed "to up their game".
A growing number of new cars are made with keyless entry systems, allowing owners to open them with the brush of a hand, as long as their actual key is nearby - for instance in their pocket.
However, thieves can fool these systems with special devices, allowing them to enter the vehicle and drive away.
Car theft is much lower than it was in the 1990s but has been rising, with keyless technology thought to be partly to blame.
In the year to March 2018, more than 106,000 offences of theft of or unauthorised taking of a motor vehicle were reported to police in England and Wales - the highest annual total since 2009.
Mike Hawes, head of the SMMT, said: "Industry takes vehicle crime extremely seriously and any claims otherwise are categorically untrue.
"New cars are more secure than ever, and the latest technology has helped bring down theft dramatically with, on average, less than 0.3% of the cars on our roads stolen.
"Criminals will always look for new ways to steal cars; it's an ongoing battle and why manufacturers continue to invest billions in ever more sophisticated security features - ahead of any regulation.
"However, technology can only do so much and we continue to call for action to stop the open sale of equipment with no legal purpose that helps criminals steal cars."