Legal experts and road safety organisations have voiced concerns about the device, called Biogarde4, which its makers claim offers a great deterrent to thieves.
Maker Biogarde says: 'If a car thief or joy-rider sets off the protective unit installed inside the vehicle he will become nauseous and be unable to breathe. The fumes released from the Biogarde4 have a truly appalling smell. The owner needs only seconds after parking the car to remove the unit's security cap and replace it with its tilt cap. The unit is then placed in its container where a thief would activate it when getting into the car.'
Its makers, who offer the product for about £5, defended the product, claiming it was not a 'booby trap' but was instead designed to 'fumigate against vermin'.
But legal expert David Faithful, of solicitor Amery-Parkes, said there was a risk the owner of any vehicle fitted with the device could be prosecuted if a thief was 'injured' by it while attempting to take a car. Faithful said: 'This is obviously a chemical weapon and there is a risk the owner of the vehicle could be liable depending on the circumstances. There is also an issue on whether this would affect a company's insurance cover.'
The Royal Society for the Prevention of Accidents added concerns about the dangers of the device affecting drivers on the move. A spokesman said: 'If something went wrong with the device while the vehicle was moving, there are concerns. If a thief got the vehicle moving, they might not be able to control it because of the smell and crash, which would clearly be a danger to other road-users.'
A spokesman for Biogarde4 said: 'Relatively speaking this isn't dangerous – unlike the hundreds of deaths and injuries directly caused by thieves driving stolen cars.'