Fitbit Aria Wi-Fi Smart Scale

Fitbit Aria Wi-Fi Smart Scale Status: beta
Beschreibung	Reverse engineering the fitbit aria wlan scale protocol
Autor:	architekt, krisha
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description

the scale

The scale offered by fitbit.com measures weight and body fat. The data is then submitted to their website and can be further analysed. It is possible to use one scale for multiple users including different accounts on fitbit.com website. The scale identifies the users by their weight and maybe by their body fat.

the master plan

We want to create an own service to analyse the data in our own way. With that we're able to bypass limits and to extend the functionality. We are maybe able to allow more users and to identify the users in a better way. Additionally the data is not transmitted any more unencrypted to a public website. One main interest is also the reversing of the protocol and maybe more...

analysis

request

• The data is transmitted with HTTP POST to http://www.fitbit.com/scale/upload
• It usually consists of 62 bytes of binary data in little endian format
  • In case there is no connection, the data is stored inside the scale and transmitted later

0                   4                   8                   C
+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
|      Ident 1      |       Battery     |     MAC Address of scale    | Firmware>
|     fixed (2)     |     in percent    | 00   1D   C9   XX   XX   XX |  e.g.   >
+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
> version |      unknown      |     Timestamp     | Number of measure-| Ident   >
>   28    |     fixed (33)    |     Sync; Unix    |   ments (here 1)  | fixed   >
+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
>         |  Elec. impedance  |   Weight in g     |  Timestamp Meas-  |   User  >
>  (2)    |   0 for guests    |                   |   urement; Unix   |  0 for  >
+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
>  ID     |  Displayed body   |    Covariance     |    Body fat 2     |
> guests  |   fat, per mil    |     as float      |                   |
+----+----+----+----+----+----+----+----+----+----+----+----+----+----+

explanation

• For guests "users id", "displayed body fat", "covariance" and "body fat 2" are set to 0.
• The covariance is also displayed inside the HTML code if you login to your account.

response

header

0                   4                   8
+----+----+----+----+----+----+----+----+----+----+
|     Timestamp     |Unit|??? |  Number of users  |
|                   |    |(0) |                   |
+----+----+----+----+----+----+----+----+----+----+

user data

0                   4                   8                   C
+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
|      User ID      |                     Always zero                           > 
|                   |                  (maybe reserved)                         >
+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
>                   |          Name of user, only first three bytes used, rest  >
>                   |                                                           >
+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
>   is filled with spaces               |    Tolerance min  |   Tolerance max   |
>                                       |                   |                   |
+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
|   Age in years    |Gen |     Height in     |    Some weight    |    Body Fat  >
|                   |der |    millimeters    |       or 0        |              >
+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
>    |   Covariance (?)  |     Some other    |     Timestamp     |
>    |  1040128544 or 0  |       weight      |                   |
+----+----+----+----+----+----+----+----+----+----+----+----+----+

padding

0                   4                   8
+----+----+----+----+----+----+----+----+
|         Padding, always zero          |
|                                       |
+----+----+----+----+----+----+----+----+

explanation

• Unit : 00: Pfund, 01: Stone, 02: Kilo
• (0) : seems to be always 32
• Tolerance max/min: last weight +/- 4kg (in our tests); used by scale to recognize users
• Gender : 02: male, 00: female

own tools

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