Laranjo et al. 2021, Apps and activity trackers and physical activity, a meta-analysis

Systematic review, meta-analysis and metaregression of 28 randomised trials (n=7,454). Interventions using smartphone apps and activity trackers produced a small-to-moderate increase in physical activity, roughly 1,850 extra steps per day at a mean follow-up of about 13 weeks. The most common behaviour-change techniques were feedback and self-monitoring, then goal-setting; adding text-messaging and personalisation made interventions more effective. Strong.