SCRATCH and sniff cards laced with the smell of cannabis will be sent around Merseyside to help people sniff out drug factories in their communities.
The cards, produced by national crime-fighting charity Crimestoppers, will be trialled in the region, which was identified as a UK cannabis cultivation hotspot.
It is hoped people who might not otherwise be familiar with the strong smell of "skunk" will be able to recognise the odour coming from neighbouring houses.
But Crimestoppers insisted there was no trace of tetrahydrocannabinol (THC), the psychoactive element in cannabis, so there was no chance of getting "high" from sniffing the cards.
Information will also be provided on other telltale signs, such as lots of cables running into properties, lights on 24 hours a day and condensation on windows.
Lord Ashcroft, who founded Crimestoppers, said cannabis farming was linked to other serious crimes.
He added: "Cannabis farms grow more than just drugs.
"Those who are cultivating cannabis tend to be involved in other areas of crime and are often involved in related gang crime and other violent crimes involving firearms.
"These individuals use violence and intimidation to carry out these crimes and endanger the lives of those around them.
"We want to help put an end to this and the funding which cultivation provides to serious organised crimes like human trafficking and gun crime."
Merseyside is one of the trial regions, along with West Yorkshire, South Yorkshire, London and Greater Manchester.
Superintendent Paul White, of Merseyside police, said: "Cannabis is not the harmless drug people think it is.
"It is the most widely used illegal drug in the UK and it is big business for criminal gangs.
"Those same gangs are also involved in violence, intimidation and gun crime, which blight the lives of decent law-abiding people.
"We are increasingly finding higher numbers of smaller-scale cannabis farms set up in houses and flats rather than industrial units.
"This means drugs are being grown right among us and collectively the public and the police need to stand shoulder to shoulder and root these drugs gangs out."
Many criminals involved in growing cannabis fiddle their electricity meters, leading to higher bills for normal households.
The cost of "energy theft" is estimated to be around £400m a year.
Call Crimestoppers on 0800 555 111.