What technical challenges are you facing in your mHealth studies?

Validity and reliability of the measuring devices under free-living conditions

• Various wearable devices show large variations in accuracy between different devices, with error margins of up to 25%
•  Commercial devices such as FitBit often rely on sensors and algorithms to measure physiological signals and activity levels, which can lead to inaccuracies in the data collected.

IMUs for actigraphy

• Compensation of noise sources due to quantization or arising from improper on-body unstable placement or misplacement and misalignment of sensors.
• Characterize missing data, create thresholds for inclusion, and define approaches for handling missing data.
• Battery Life: Another technical challenge encountered when using commercial devices for research studies is battery life. Many of these devices require frequent charging, and as such, may limit the amount of data that can be collected over a certain period of time.

Wearables with GPS - although they allow the user to look at GPS information live, there is usually not a way to download a log of all GPS movements. 

Restrictive OS-level APIs and Play Store policies that make it hard to collect GPS type of data. Require the development of in-house apps.