Background:
Exposure to secondhand smoke (SHS) is a cause of severe childhood illness. Accordingly, governments and health authorities recommend never smoking in homes where children live, and a range of behaviour change interventions to promote smoke-free homes have been developed. Air quality feedback, where information about SHS-related air pollution in the home is provided to smoking parents, has been used in behaviour change interventions with some success.

Objectives:
To develop a remote internet-based air quality feedback intervention to promote smoke-free homes, and to test that intervention in five centres across four European countries.

Methods:
Inclusion criteria were homes in which someone smokes indoors and where a child aged <16 years spends at least one night per week. Internet-connected Dylos DC1700 monitors were developed and installed in homes for 30 days. The first (baseline) and last (follow-up) seven days served as comparators, while SMS, email and telephone feedback was provided between, from days 8–23. The primary outcome measure was the change in mean fine particulate matter (PM2.5) between baseline and follow-up, while secondary outcome measures included the number of homes in which PM2.5 concentrations declined and the change in time spent over the World Health Organisation’s guideline limit for PM2.5 concentrations indoors.

Results:
The median change in PM2.5 concentration between baseline and follow-up was -4.1µg/m³ (19%, p=0.008). About two-thirds (57/86; 66%) of participating homes experienced declines in measured SHS throughout the study. Time spent over the WHO guideline limit fell by a median of 3.3%.

Conclusions:
The measuring-for-change intervention led to reduced levels of SHS in most homes where it was tested, but few homes became wholly smoke-free throughout the study period.