Diesel Guard uses the same technology found in musical greeting cards and provides drivers with an audible warning when they open their fuel filler caps.
It is estimated that 120,000 UK motorists fill their cars' tanks with the wrong fuel every year. It can cost up to £3,000 to put right and can put a car out of action for days.
A spokesman for UK FuelGuard, the company which makes the device, said: 'When filling up at the petrol station Diesel Guard reminds you that your car runs on diesel with an audible warning message, so that even if you are not concentrating, you are unlikely to fill up with the wrong fuel.'
The matchbox-sized gadget fits on the inside of the fuel filler flap with adhesive tape. Covered in plastic, it is protected against fuel leakage and is activated by light sensors once the fuel cover is opened.
The gadget would be particularly useful for fleets running pool cars or with vehicles swapping hands on a regular basis, such as rental fleets.
A spokesman said: 'Diesel Guard can offer considerable savings in costs when fitted by fleet and rental users, protecting against the misfuelling of vehicles by users unfamiliar with the correct fuel. It is simple to fit prior to delivery or can be retro-fitted.
'Unlike other misfuelling prevention systems Diesel Guard is simple to fit, requiring no rewiring and installation costs.'
The number of call-outs taken by the AA for misfuelled vehicles has surged by about 10,000 per year since 1998. Last year the AA responded to 44,000 call outs by motorists misfuelling.
DIESEL Guard is the brainchild of Wirral inventor Chris Bibby. Bibby designed the gadget after filling his vehicle with the wrong fuel and he is marketing the product to fleets with the help of his nephew Kirk Eden.
Previous projects for Bibby include working for a construction company and with a car sales firm. The AA Trust launched a campaign earlier this year to promote awareness against misfuelling.
As part of the campaign, advice cards will be handed out at more than 5,000 petrol stations across the UK to warn of the dangers of putting the wrong fuel in a car.