The problem of underage smoking looks to have worsened, as some schools turn to detection devices to help them smoke out offenders.
Last year, more than 6,200 smokers below the legal age of 18, including some in primary school, were caught. This was about 17 per cent more than the 5,311 in 2013, according to data from the Health Sciences Authority (HSA).
Most underage smokers caught were 15 to 17 years old and the rise in numbers could be because of greater enforcement, said an HSA spokesman.
But a 36-year-old teacher who spoke to The Straits Times on condition of anonymity said she has noticed a growing number of student smokers in her neighbourhood secondary school, where she has taught for 14 years.
There are those who pick up the habit in primary school, smoking as many as 10 sticks a day by the time they enter secondary school. Some light up in school, with habitual offenders using hidden corners or toilets to take a puff, she said.
Several schools, such as Greenridge and Chestnut Drive secondary schools, have used "smokerlysers" - portable devices that measure carbon monoxide, a by-product of cigarette smoke - to monitor if students smoke.
Newer versions of these devices can detect cigarette use from as far as two days back. A Health Promotion Board (HPB) spokesman said these carbon monoxide meters are used in its smoking cessation programme in schools.
Over in Choa Chu Kang, Regent Secondary School plans to install cigarette smoke detectors in the common areas of five of its male toilets. It wants detectors that can log the exact location and time when someone smokes, and send an alert to the school's general office and a message to a staff member's mobile phone.
"The initiative is one of the school's efforts to promote deterrence," said Regent's vice-principal Sheree Chong, adding that it also holds anti-smoking talks.
Mr T.C. Lim, 48, whose company distributes cigarette smoke detectors, said such products have been in Singapore for more than a decade, but demand from schools has been low as most found the device too costly. He began getting enquiries from schools last year. A toilet with four cubicles should ideally have two detectors, he added, each of which can cost $500 to $700.
The effectiveness of such efforts remains to be seen, as "it would take more influence than detection to curb the problem of underage smoking", said Ms Gracia Goh, deputy director of the Singapore Children's Society. Its Youth Centre runs anti-smoking campaigns and has encountered smokers as young as eight.
"Influence by family, friends and community has a much stronger impact for them," she said, referring to young smokers.
Take Varun, a 17-year-old student, who took his first puff two years ago "because all my friends were smoking". Now the Institute of Technical Education student, who declined to give his full name, is a habitual smoker but his family does not know.
Persons below 18 caught using, buying or possessing tobacco products can be fined up to $300. First-time offenders can have the fines waived if they finish an online smoking cessation module.
The HPB said it works closely with the Ministry of Education to discourage youth from experimenting with tobacco products.