A loud hailer is being used to embarrass those caught dropping litter on the streets of Preston city centre.
Undercover colleagues tip off litter officer Sonia Scowcroft
The city council is using the speaker system to target litter louts, letting them know they have been seen and urging them to pick up their rubbish.
The We Are Watching You campaign was the idea of the city's litter education officer Sonia Scowcroft.
Her undercover colleagues keep an eye out for litter-droppers, before Sonia singles them out on the speaker.
The system is based at the city's Flag Market and is used randomly to "surprise" offenders.
The market sound system is used to single-out litter louts
Ms Scowcroft told BBC News: "We find that if we do it without warning it is more effective.
"My colleagues tell me via a radio system when someone has dropped litter and I let them know, over the speaker, that they have been seen.
"People usually drop litter, sometimes within a metre of a bin, thinking that no-one is watching. This system means that we can make it clear that they are being seen and they are usually embarrassed.
"We have had instances where people go back and pick their litter up. We make people think twice - and it's been very effective."
Street-cleaners in the city say that the campaign has meant less litter on the streets - and more in the bins.
It costs the council £1.4 million every year to clean up Preston's streets.