This pilot study data was collected to test the feasibility of a new methodological approach that could help to investigate how environmental behaviour (transport behaviour, energy consumption, food consumption, goods consumption, wasting) dilemmas can be overcome on an individual level in real life by using smartphones to collect daily behavioural data in a field-experimental setup. The data includes information on the above-mentioned behaviour based on survey responses, GPS records, barcode scans and electric meter counter images. The data were collected in June 2017 daily over two weeks from 20 study participants of whom 12 were female and 8 male. Moreover, 13 were University students and 7 had a professional background. The two field-experimental interventions were implemented in the second week of data collection and included (1) behavioural targeting (individualised message nudges based on past behaviour) and (2) social monitoring (messages that allowed participants to monitor their own and others' environmental performance). The 20 study participants were randomly and evenly assigned to the two field-experimental interventions. Given the lack of a control group (due to financial limitations to include more study participants), the first week serves as a reference point for assessing treatment effects. Additional to the smartphone-based daily data, basic socio-demographic and attitudinal data were collected through an initial online survey. This data includes information on study participants' gender, age, financial situation and environmental attitudes (e.g. on climate change and recycling). Moreover, a final online survey was conducted after the two-weeks smartphone-based data collection to assess study participants' experience with the study design. The study participants were compensated with a 50 GBP Amazon vouchers for their study participation. This project is a pilot (feasibility) research project to study environmental behaviour (transport behaviour, energy consumption, food consumption, goods consumption, waste production) in real life situations by using smartphones to collect daily behavioural data over two weeks in a field-experimental setup. Demonstrating the feasibility of a novel approach to studying environmental behaviour will enable us to subsequently raise funds for and conduct a major study with additional field-experimental treatments and a larger, more representative sample. For the pilot project, 20 study participants will be recruited among University students and members of staff. They will be assigned to two groups to study to what extent two experimental treatments can alter environmental behaviour: (1) behavioural targeting: study participants' past behaviour will be analysed to deliver individually tailored tips on how they can increase the sustainability of their behaviour, testing nudge theory assumptions; (2) social monitoring: study participants (anonymised) will be able to monitor each other's environmental behaviour through the smartphone application, testing social influence theory assumptions. Data collection will include short survey question responses (e.g. type of transport used and why) on environmental behaviour, GPS coordinates, electric meter data and barcode scans. In the first week, the data will be collected without a field-experimental intervention. In the second week, the 20 study participants will be split into two groups of 10 in order to receive one of the two field-experimental treatments.

EpiCollect 5 Smartphone application was used for data collection. The app operated on Android and iOS phones. The data collection fields implemented in the app and used in the project are free text entry (username), multiple choice and single choice responses to survey questions (see questionnaire), images (of electric meter counters, voluntarily), GPS coordinates (voluntarily), barcode scans (voluntarily). The users could collect the data throughout the day and would then upload the data actively to the server in the evening via the EpiCollect 5 app. All data was time-stamped. Furthermore, initial and final online survey data was collected before and after the smartphone-based data collection. The online survey data was collected via Q-set. The initial survey data contains single choice survey responses. The final survey data contains single choice survey responses as well as free text entry data (see questionnaires).