In today's world, physical activity is gaining more importance, not only in academic community, but also with the general public. Nowadays, many students expect to see involvement of new technologies in school such as smartphones, tablets, and computers. The level of physical activity is very easily affected by various external influences such as smartphone apps, which may be ideal in increasing physical activity. Smartphone apps are considered motivational tools in increasing physical activity. The aim of the study was to analyse the role of smartphones in increasing physical activity in secondary school students. The study group was chosen purposively to meet the aim of the study. The following criteria applied: a) participants should not have health issues; b) participants should be from the same year of students. The group consisted of 113 secondary school students [(Male control group n = 30 (26.54 %); Male experimental group n = 25 (22.12 %); Female control group n = 30 (26.54 %); Female experimental group n = 28 (24.80 %)]. The current level of physical activity was detected by using the smartphone app - Samsung Health [(Samsung Electronics Co., Ltd.; Suwon, the Republic of Korea; Android 5.17.1.003; iOS 1.5)]. Two 14-day challenges were created to increase physical activity in the participants. To determine the statistical significance of 2 control groups (n = 60, 53.08 %) and 2 experimental groups (n = 53; 46.92 %) we applied the Wilcoxon Signed-rank Test (Wtest p < 0.01, p < 0.05). To verify 4 independent study groups, we applied the Mann-Whitney U-test (Mwtest p < 0.01, p < 0.05). The material and practical significance was evaluated by using the effect size coefficient (r) (r = 0.10 - small, r = 0.30 - medium, r = 0.50 - large effect size). The first 14-day challenge resulted in improvements in both control and experimental groups of secondary school students (p < 0.01). After 28-day challenge, we recorded the improvements in the female experimental group (p < 0.01), male control and experimental groups (p < 0.01) and female control group (p < 0.05). When comparing the independent study groups, we recorded improvements, which were significant at 1.00 % and 5.00% level. Secondary school students are increasingly using smartphone apps routinely in more areas of their personal lives. Smartphone apps aimed at increasing physical activity are effective in helping secondary school students to achieve the required physical activity level. Our study provides evidence that the technique of challenges used in the smartphone app - Samsung Health significantly (p < 0.01, p < 0.05) increase the physical activity level of the secondary school students. According to our results, we recommend using the smartphone app - Samsung Health as a motivational tool in increasing the physical activity in secondary school students.