Indeed, almost all trackers come with notifications and in the study notifications are included in the wearable-based intervention.
The result of 50% larger effects in multifaceted interventions versus wearable-based interventions is from a study by Brickwood (2019). In this study, they distinguish wearable-based interventions (interventions that included tools such as regular emails, text messages, online algorithms, or smartphone apps) and multifaceted interventions (using in addition established behavioral change techniques such as group or individual counseling or information sessions, financial incentives, or telephone counseling).
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6484266/
Impressive results, but I think it is important to keep in mind that most of the examined studies in this meta-analysis combined wearable activity trackers with an intervention. The effect of only using a wearable is probably much smaller and the duration of the effect is unclear.
From the limitations section of the discussion:
“Although this umbrella review provides strong assurance of the efficacy of wearable activity trackers in increasing physical activity, few of the systematic reviews and meta-analyses examined the effectiveness of wearable activity trackers alone. […] the multifaceted interventions yielded effects around 50% larger than those using wearable activity trackers alone.”
The result of 50% larger effects in multifaceted interventions versus wearable-based interventions is from a study by Brickwood (2019). In this study, they distinguish wearable-based interventions (interventions that included tools such as regular emails, text messages, online algorithms, or smartphone apps) and multifaceted interventions (using in addition established behavioral change techniques such as group or individual counseling or information sessions, financial incentives, or telephone counseling). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6484266/