For roughly pound;100 per cubicle, schools can now install a super-sensitive smoke alarm that will set bells ringing in the office every time someone decides to ignore their health education lessons and light up.
"It's the girls who seem to be the worst offenders," says Brent Dunleavey of Radal Technology, the inventors of the (wait for it)Cig-Arrete smoke-detector. "They don't want to smoke out in the open."
Committed wheezers will always congregate behind the bike sheds for a drag. But the Burnley firm says that getting rid of smoking in the toilets can reduce peer pressure on younger pupils, bullied or mocked by older children into taking up the filthy weed.
"Hopefully over a few years, you can filter smoking out of schools," says Brent.
Chesterfield high school in Crosby, Merseyside, has fitted the tamper-proof devices in one set of girls' loos.
Deputy head Fred Cowell said that after going off a few times they had done the trick as a deterrent, and could now be installed in other toilets.
"Girls were smoking as soon as they arrived in school," he said. "It's only a small number but it was disturbing other youngsters who don't want to suffer the effects of passive smoking.
"More girls smoke than boys and for girls it's more of a social activity. Some boys smoke but they go further away - it's more of a game to them and they don't mind a chase. Girls want to get together with their friends."
The alarm filters out other particles in the air - such as dust sent swirling by an opening door - to detect only smoke. It was originally developed for plants such as solvent factories where smoking presented a health risk, and for the growing number of non-smoking offices.