Fitbit detects pregnancy

A Fitbit device has detected a pregnancy before the expectant mother knew. The couple posted a question online that the device was reporting an unusual heart rate reading asking for a way to recalibrate the device or for a replacement. A standard test showed that the woman was two months pregnant.

Great. Can they detect lying too? Can Fitbit results be subpoenaed and used against their owner? How long until we all have devices like these and only weird people don't know their current heart rate and daily calorie burn rate?