Recovery is a key concept in surgery, yet it is difficult to define or measure. Assessing postoperative recovery traditionally uses short-term surrogate measures, such as hospital length of stay and complications 1 ; however, these outcomes fail to capture the perspective of patients who equate recovery with resuming usual activities after hospital discharge. 2,3 It is thus essential that patientcentered recovery assessments incorporate data that evaluate physical function beyond the immediate postoperative period.The use of smartphone activity sensors provides an opportunity to capture physical activity data after surgery, enabling the extended assessment of patients along their recovery trajectory. In a prospective cohort study in this issue of JAMA Surgery, Panda et al 4 tested the hypothesis that metrics derived from a smartphone accelerometer would be able to detect differences in physical recovery in patients undergoing cancer surgery. Their findings support that, among patients with a postoperative event (ie, complication and/or reoperation), accelerometer data captured a decrease in daily activities up to 6 weeks after surgery. Similarly, fewer of these patients achieved 60 minutes of daily exertional activity compared with patients without a postoperative event. The methodological pitfalls of the study include a risk of selection bias (only 57% of eligible patients downloaded the smartphone application) and attrition bias (accelerometer data were missing for a median of 22% of days). Also, there is no mention of a