An 11ft behavioural experiment turned mundane waste disposal into visible social proof—tripling ashtray use from 27.6% to 67.3%
Cigarette butts are the most common form of litter worldwide—45 billion discarded annually. The barrier isn’t ignorance; it’s invisibility. Correct disposal is a private act with no visible consequence or social reinforcement. When no one notices the right behaviour, there’s no social norm to follow.
Traditional approaches, like more ashtrays, warning signs, or fines, underperform because they instruct people what to do but fail to show that others are doing it.
The Behavioural Science team led by Niklas Lanninge identified the core issue: people change when the environment makes the right behaviour visible, not when they’re simply told to change.
The solution? An eleven-foot blue sculpture in a central square. Every time someone disposed of a cigarette correctly, it emitted a puff of smoke—an ancient signal repurposed for modern urban cleanliness.
The logic: social proof, made visible. Each smoke signal transforms an individual action into a public cue. Motion sensors detect the cigarette and trigger a brief, theatrical burst — a playful reward for the right choice. Smokers began to pause, watch, and gather for the next puff.
Three critical factors:
The results: Cigarette butts in ashtrays tripled — from 27.6% to 67.3%. The intervention created a new social norm through repeated, visible participation.
The Business Case: Cigarette litter creates ongoing clean-up costs and environmental damage. Enforcement through fines is labour-intensive and strains citizen relationships. The smoke signal machine changes behaviour without policing, reduces costs, and turns compliance into a positive experience. A single installation influences thousands of daily decisions — an exceptionally low cost per behaviour change compared with typical awareness campaigns.
Have you seen other nudges that make invisible good behaviour visible?
Share your thoughts: hello@green-nudges.com
From Elina Carlstein, Communications Officer and Behavioural Strategist at the City of Malmö, who used behavioural science to tackle cigarette litter through visible social feedback.
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