Background: Daily-life walking speed, which is a critical health indicator in older adults, can be measured using smartphone GPS technology. Although this method is becoming more widely accessible, it is restricted to outdoor walking. In contrast, accelerometers can capture walking speed indoors; however, there is limited information on the comparability of daily-life walking speed data between these two techniques. Objective: This study aimed to compare daily-life walking speeds measured using a smartphone GPS app and an ankle-band accelerometer. Methods: Participants were recruited from a previously selected cohort of community-dwelling older adults. Their daily-life walking speed was assessed using a smartphone app and ankle band accelerometer. Data from the two devices were matched based on simultaneous recordings, and agreement between the walking speeds was evaluated using the intraclass correlation coefficient (ICC) and a Bland-Altman plot. Results: The GPS app consistently recorded a faster walking speed than the ankle-band accelerometer. This data suggests that a correction is necessary when comparing the daily-life walking speed between these two devices. Conclusions: The GPS consistently recorded a faster walking speed than that measured by the ankle-band accelerometer, suggesting a correction is necessary when comparing the daily-life walking speed between these two devices. Clinical Trial: None.