Smell device on trains nabs graffiti thugs

Graffiti vandals are being caught in the act thanks to a new vapour-sensing system installed on Sydney trains.

The NSW government is running a trial of the Mousetrap device, an electronic chemical sensor that detects the smell of spray paint or marker pens and then immediately alerts train guards.

More than 30 offenders have been arrested so far.

"We know it's early days for Mousetrap but its success has been in allowing Sydney trains to move from a strategy of removing graffiti to one where we stop it as it happens," said Sydney Trains boss Howard Collins.

The government spent $34 million last financial year removing graffiti from the Sydney Trains network, up from $30 million the year before.