PARIS, March 15 -- Could a smell so awful it's intolerable be a more effective deterrent than any conventional anti-theft device? With this in mind, a new kind of bike lock has been developed, emitting a gas with a smell deemed unbearable, both to scare away thieves and to alert passers-by.

Every year in France, between 400,000 and 580,000 bicycles are stolen, according to various surveys carried out in recent years by the Ministry of Transport and declarations made to insurers.

Faced with this scourge, a young French chemical engineering student, Aiko Leroux, has launched a novel innovation: a bike lock that emits a foul smell in the event of a theft attempt.

Called CactUs, this anti-theft device differs from traditional solutions in ...