This study by Leimhofer et al. evaluates smartphone sensor data and software data streams available across different mobile platforms (Android and iOS), and their usage for monitoring and predicting depression. To do so, Leimhofer et al. conducted an umbrella review of existing systematic reviews published between 2019 and 2024 to identify which smartphone sensor modalities (such as accelerometer, GPS, or app usage) have been used in depression monitoring. They then used the PhoneDB database to check how available these hardware sensors are on Android vs. iOS devices from 2014-2024 to compare cross-platform availability. They found 16 hardware and 3 software data streams used in the reviewed literature, including accelerometers, GPS, cameras, app usage, and call logs. The availability of sensors like accelerometers, GPS, cameras remained consistent on both Android and iOS over time, but other sensors such as gyroscopes, step counters, and barometers increased especially on Android over the years. As such, Leimhofer et al. conclude that while multiple data streams are becoming more widely available, significant variation in mobile hardware and software remains a barrier to reliable and generalisable depression-prediction systems. They also emphasize the need for efforts to streamline sensor data access and standardise methods across platforms if these systems are to be deployed at scale.