The Silent Killer was a design solution to engage and motivate long-term behaviour change; to persuade people to act to avoid the devastating effects of unsafe gas work. The test campaign ran in the North West of England between October 2012 and February 2013. This was the first time Gas Safe Register had aimed to persuade people to change their behaviour rather than simply raise awareness of the dangers of unsafe gas work. In just five months, Gas Safe achieved a staggering 300% increase in the number of higher risk households having annual gas safety checks. This equates to an additional 53,424 households in the North West protecting themselves from the devastating impact of unsafe gas work and appliances. All the more impressive is that this was not a trend recorded across other UK regions, which remained relatively flat. Over 30,000 unique visitors to the website were recorded over the five-month campaign period, three times the target level set. Another 2,600 households signed up for an annual safety check. There were 8,500 registered engineers reached by the campaign and 21,000 members reached each month through the National Landlords magazine. The Health and Safety Executive is supporting national roll-out from August 2013.