The Digital Detox study is designed as a randomized controlled trial (two unblinded parallel groups) to examine the effects of reducing smartphone screentime on mental health. After giving informed consent, participants will be screened for eligibility. Inclusion criteria are adult subjects (greater-equal 18 years) using their smartphone daily for 3 hours or more, with sufficient German skills and no ongoing psychotherapy, psychological or psychopharmacological treatment. For eligibility screening, participants have to upload a screenshot of their smartphone screen time of the last week, have to state about mental health disorders (self-report) and their sociodemographic variables (age, gender, country of residence, education and professional status, urban/rural nature of place of residence), and have to fill out the following questionnaires: depressive symptoms (PHQ-9), well-being (WHO-5), sleep quality (ISI), stress (PSQ-20), loneliness (three-item loneliness scale), physical activity, and smartphone usage behavior.

If the inclusion criteria are met, participants will be randomized to the intervention or control group. The intervention consists of a three-week screen time reduction to a maximum of 2 hours per day for 3 consecutive weeks. The control group continues to use their smartphones as usual during this time. At the beginning of the study (=baseline T0), all participants will complete the following primary outcome measures (depressive symptoms (PHQ-9), well-being (WHO-5), sleep quality (ISI), stress (PSQ-20)) and secondary outcome measures (loneliness (three-item loneliness scale), craving (CEQ-F), physical activity). Both groups will also complete items on loneliness and physical activity twice during the intervention (after the first and second week of the intervention) to monitor changes in these variables during the intervention. After the three weeks of intervention (post-intervention T1), both groups will again fill out the the same outcome measures as for T0. After the 3-week intervention, there are no further restrictions regarding the participants' smartphone screen time. Follow-up (T2) will be after 3 more weeks and the same outcome measures as for T0 and T1 will be collected.

The weekly smartphone screen time is assessed via self-reporting and screenshot upload. Information is also provided on the weekly activations of the smartphone and a screenshot is uploaded of the most frequently used apps. All data is collected weekly for the previous week.

The study will be performed entirely via a smartphone app (ESMIra), which is designed especially to run longitudinal studies.

Primary hypotheses:

• H1: Reducing smartphone use to a maximum of 2 hours/day over 3 weeks leads to a difference in the depressive symptoms of the intervention participants before and after participating in the intervention.
• H2: Reducing smartphone use to a maximum of 2 hours/day over 3 weeks leads to a difference in the the sleep quality of the intervention participants before and after participating in the intervention.
• H3: Reducing smartphone use to a maximum of 2 hours/day over 3 weeks leads to a difference in perceived stress of the intervention participants before and after participating in the intervention.
• H4: Reducing smartphone use to a maximum of 2 hours/day over 3 weeks leads to a difference in the well-being of the intervention participants before and after participating in the intervention.
• H5: The reduction in smartphone use to a maximum of 2 hours/day over 3 weeks led to a difference in depressive symptoms between the control and intervention groups at the post-intervention time point.
• H6: The reduction in smartphone use to a maximum of 2 hours/day over 3 weeks led to a difference in sleep quality between the control and intervention groups at the post-intervention time point.
• H7: The reduction in smartphone use to a maximum of 2 hours/day over 3 weeks led to a difference in perceived stress between the control and intervention groups at the post-intervention time point.
• H8: The reduction in smartphone use to a maximum of 2 hours/day over 3 weeks led to a difference in well-being between the control and intervention groups at the post-intervention time point.

The study employs a convenience sampling method to recruit participants. Recruitment channels include social media accounts of the university and the department (Instagram: istokay.at, unikrems, and X (formerly Twitter): @PsychiUniKrems), where posts and story updates will provide information about the study. Additionally, emails will be sent to universities, universities of applied sciences, and other educational institutions, and flyers will be distributed. These materials will inform potential participants about the study's purpose and procedures.

Interested individuals can access the study page on ESMira via a link or QR code. There, they provide electronic consent before completing the screening questionnaire, which assesses the study's inclusion and exclusion criteria.

Control group will be offered to also participate in the intervention after study completion.

Data Collection

All data collection and communication with participants will take place exclusively through the ESMira research application. ESMira is compatible with all smartphones and was specifically developed for scientific studies, particularly those with a longitudinal design. The app allows for the administration of questionnaires at pre-specified time points and facilitates fully anonymous communication with participants.

A permanent internet connection is not required for using ESMira. Completed questionnaires are stored locally on the app and automatically uploaded once an internet connection becomes available. Research data is stored in encrypted form on a secure server at the University for Continuing Education Krems. Participant anonymity is ensured through a randomly generated user ID (12 alphanumeric characters, e.g., 4mZm-F8vN-5Vyk) assigned by ESMira.

For more information about ESMira, visit: https://github.com/KL-Psychological-Methodology/.

Data Security and Storage:

In accordance with Article 32 of the DSGVO, data security measures will be implemented to ensure the protection and confidentiality of participant information. The data is stored on a local server and is protected against unauthorized access. Unauthorized reading, copying, modification or deletion is therefore not possible. Furthermore, the data is only collected and stored in pseudonymized form. The personal data is only stored for the duration of the study. After that, it is only stored in a completely anonymized form.

Used questionnaire:

Screening only:

Sociodemographic variables: Age (in years), gender, country of residence, highest completed education, current educational/employment status, urban/rural classification of residence.

Mental health (self-report):

Do you have a mental health condition for which you are currently receiving treatment? (yes/no) Are you currently taking medication for a mental health condition? (yes/no) Smartphone usage: Do you use your smartphone for an average of ≥3 hours per day? (yes/no)

Assessed at screening and all subsequent time points (T0, T1, T2):

Depressive Symptoms (PHQ-9) The Patient Health Questionnaire (PHQ-9) is used to assess depressive symptoms in its validated German version, consisting of 9 items.

Well-being (WHO-5) The validated German version of the World Health Organization Well-Being Index (WHO-5) is used to assess participants' well-being and consists of 5 items.

Sleep Quality (ISI) :

The Insomnia Severity Index (ISI) is used in its validated German version to assess the quality of sleep and consists of 7 items.

Stress (PSQ-20): Stress is assessed using the German version of the short form of the Perceived Stress Questionnaire (PSQ-20), which consists of 20 items.

Loneliness (3-Item Loneliness Questionnaire): Loneliness is assessed using the German version of the Three Items Loneliness Scale, consisting of 3 items.

Physical activity: "On how many of the last 7 days were you physically active for at least 60 minutes?" and "How many minutes did you spend doing sport in the last 7 days?" Craving (CEQ-F) [not in screening]: Craving is measured using the Craving Experience Questionnaire (CEQ-F) in the German version, for behavioral addictions and smartphone use in particular, and consists of 9 items.

Smartphone use (self-report and upload of screenshots of screentime over the last week, activations, and the most frequently used apps).

Inclusion Criteria:

• healthy subjects
• greater-equal 18 years
• sufficient German skills
• using a smartphone daily 3 hours or more
• no ongoing psychotherapy, psychological or psychopharmacological treatment

Exclusion Criteria:

• Age under 18 years
• insufficient German skills
• Smartphone use less than 3 hours per day
• ongoing psychotherapy, psychological or psychopharmacological treatment