Looking for fitbit-like tracker / sensor OEM Style.

[xiaxk]

Hi there,
Can someone please advise where one can find a fitbit-like gadget that one can use for a project which basically does the following:

- Tracker that has sensors such as accelerometer/ gyroscope
- Bluetooth module
- Built-in battery
- Communicate via Bluetooth to a smartphone
What is this called? Tracker? Motion Detector?

I understand that these are used in all wearable devices such as fitbit, gear etc.

My only expectation from this instrument would be to capture the sensor data, store it and send it via bluetooth to a smartphone; all the computation is done by the smartphone.

I want to be able to buy it so I can carry some custom projects; these projects are based on detecting/measuring/analysing human motion to arrive to specific conclusions.

For example, the module shown on this webpage:

https://www.microcontrollertips.com/inside-fitbit-charge/
**broken link removed**
https://www.ifixit.com/Teardown/Fitbit+Flex+Teardown/16050

Would reallly appreciate any kind of informationi / referrals and if someone can point me in the right direction where to start from.

Hence looking for
- websites / forums
- videos
- retailers / online shops
- manufacturers

Thank you.