How this whole stuff really work
First of all, for now, Sensie requires latest Lumia phones sporting SensorCore technology and Cyan firmware update (For Lumia 1520 owners - WP 8.1 DP without Cyan doesn't work).
SensorCore is a combination of hardware and software that enables to get move, activity and steps information from your phone without significantly affecting your battery life. It requires a chipsets from the new Snapdragon line.
Snapdragons 200, 400, 600, and 800 collect data from WiFi spots, GPS towers, gyroscope and other sensors while Lumia firmware makes them available to developers. All this is done without GPS and OS running so it needs a minimum of power.
Certainly there are limitations:
- position is recorder every 5 minutes and 500m distance
- steps and activity information is not realtime to get rid of the noise information
- it requires Wi-Fi to be on
- known places are guessed from your daily behaviour, so it takes a few days to determine where is your home and workplace
- the accuracy in urban areas is better
So, for the most accurate results:
- keep Wi-Fi on
- keep Wi-Fi Sense on
- if you, in parallel, use another app that uses GPS (map, nav, etc.), the recorded positions are more accurate
More here: https://www.qualcomm.com/products/snapdragon/sensors
SensorCore itself keeps a history for 10 days. If you start Sensie for the first time, you will immediately get 10 days data (if you have Motion Data turned on in settings).
Sensie puts all the data into database, so Sensie history is virtually unlimited.
Sensie doesn't send any data to cloud or 3rd party services. You may backup your local database to your own OneDrive anyway.