Haywatch

• Haywatch
  • Hello Haylou
  • Watch features
  • Device communication
    • General command structure
    • Pairing
    • Unpairing
    • Battery
    • Firmware
    • Date and time
    • Pulses
    • Unit settings
    • Alert messages
    • Weather

Haylou Smart Watch 2 (LS02) reverse-engineering (RE-ing) project

Note that this is the result of RE-ing the (unofficial) Hello Haylou app (reasons of this explained below).

Since nothing technical popped up about this watch model on the Internet (aside from usual smart-watch articles and some apps), I've decided to document it as deeply as I can.

Hello Haylou

The official Haylou app, the one expected to be used with this watch, is quite bad (just check reviews/comments on the provided Play Store link). Furthermore, the core sources of the app, the vast majority of its code, is native, which complicates the RE process.

Therefore, one of the best alternatives (might be the only one?) is the mentioned Hello Haylou app. This app appears to be developed by a Hungarian dev team named Tibor Borsos, who have also developed similar apps for other smart watches.

There is evidence of all the claims made on the app's decompiled code: some debug logs contain Hungarian text, and several class/type names start by MiBand*, suggesting this app's source might contain copy-pastes of another app supporting Xiaomi Mi Band smart-watches, which they have actually made.

It's noteworthy to mention that the app supports 10 different Haylou smart watch models, but this RE-ing project is exclusively focused on the LS02 model.

The app seems to be developed on Kotlin (aside external libs used within it), and it appears to be the result of their own RE-ing of the watch and the official app.

The dev team use their own servers (https://hello-haylou.web.app/) for storing watch firmware files and images. However, this isn't something really useful for this project since LS02 watches do not support custom watch-face firmware, thus have no files for them in this servers.

Some parts of the app suggest that they have to RE the watch/the official app. First of all, many responses sent by the watch are ignored or only small parts of their contents are actually used. Furthermore, commands are often constructed by taking base byte-array (which appears to be a dump of an actual command) and modify the key parts of it.

Watch features

TODO

Device communication

Communications with the corresponding device are a key component of part of the watch's features.

The watch's UI options are severely limited, this being particularly clear when compared to the options the device is expected to request and/or receive from it.

The watch can communicate through BLE/GATT functionality. While the watch expects to connect to a mobile phone (furthermore, it expects and encourages the user to use the official app) any BLE-capable device can do so.

Watch recognition is just based on the device's name, since all LS02 watches appear as Bluetooth devices named "Haylou Smart Watch 2". The app simply tries to connect with devices with that exact name (and the same goes for the other supported watch models).

These are all the available GATT characteristics:

Characteristic { uuid: 00002a05-0000-1000-8000-00805f9b34fb, service_uuid: 00001801-0000-1000-8000-00805f9b34fb, properties: INDICATE }
Characteristic { uuid: 00002a19-0000-1000-8000-00805f9b34fb, service_uuid: 0000180f-0000-1000-8000-00805f9b34fb, properties: READ | NOTIFY }
Characteristic { uuid: 000033f1-0000-1000-8000-00805f9b34fb, service_uuid: 000055ff-0000-1000-8000-00805f9b34fb, properties: READ | WRITE }
Characteristic { uuid: 000033f2-0000-1000-8000-00805f9b34fb, service_uuid: 000055ff-0000-1000-8000-00805f9b34fb, properties: NOTIFY }
Characteristic { uuid: 000034f1-0000-1000-8000-00805f9b34fb, service_uuid: 000056ff-0000-1000-8000-00805f9b34fb, properties: READ | WRITE_WITHOUT_RESPONSE }
Characteristic { uuid: 000034f2-0000-1000-8000-00805f9b34fb, service_uuid: 000056ff-0000-1000-8000-00805f9b34fb, properties: NOTIFY }
Characteristic { uuid: 00006001-0000-1000-8000-00805f9b34fb, service_uuid: 000060ff-0000-1000-8000-00805f9b34fb, properties: READ | WRITE_WITHOUT_RESPONSE }
Characteristic { uuid: 00006002-0000-1000-8000-00805f9b34fb, service_uuid: 000060ff-0000-1000-8000-00805f9b34fb, properties: NOTIFY }
Characteristic { uuid: 00006101-0000-1000-8000-00805f9b34fb, service_uuid: 000061ff-0000-1000-8000-00805f9b34fb, properties: READ | WRITE_WITHOUT_RESPONSE }
Characteristic { uuid: 00006102-0000-1000-8000-00805f9b34fb, service_uuid: 000061ff-0000-1000-8000-00805f9b34fb, properties: NOTIFY }
Characteristic { uuid: 0000b003-0000-1000-8000-00805f9b34fb, service_uuid: 000055ff-0000-1000-8000-00805f9b34fb, properties: READ | WRITE }
Characteristic { uuid: 0000b004-0000-1000-8000-00805f9b34fb, service_uuid: 000055ff-0000-1000-8000-00805f9b34fb, properties: NOTIFY }
Characteristic { uuid: 0000ffd1-0000-1000-8000-00805f9b34fb, service_uuid: 0000d0ff-3c17-d293-8e48-14fe2e4da212, properties: WRITE_WITHOUT_RESPONSE }
Characteristic { uuid: 0000ffd2-0000-1000-8000-00805f9b34fb, service_uuid: 0000d0ff-3c17-d293-8e48-14fe2e4da212, properties: READ }
Characteristic { uuid: 0000ffd3-0000-1000-8000-00805f9b34fb, service_uuid: 0000d0ff-3c17-d293-8e48-14fe2e4da212, properties: READ }
Characteristic { uuid: 0000ffd4-0000-1000-8000-00805f9b34fb, service_uuid: 0000d0ff-3c17-d293-8e48-14fe2e4da212, properties: READ }
Characteristic { uuid: 0000ffd5-0000-1000-8000-00805f9b34fb, service_uuid: 0000d0ff-3c17-d293-8e48-14fe2e4da212, properties: READ }
Characteristic { uuid: 0000ffd8-0000-1000-8000-00805f9b34fb, service_uuid: 0000d0ff-3c17-d293-8e48-14fe2e4da212, properties: WRITE_WITHOUT_RESPONSE }
Characteristic { uuid: 0000ffe0-0000-1000-8000-00805f9b34fb, service_uuid: 0000d0ff-3c17-d293-8e48-14fe2e4da212, properties: READ }
Characteristic { uuid: 0000fff1-0000-1000-8000-00805f9b34fb, service_uuid: 0000d0ff-3c17-d293-8e48-14fe2e4da212, properties: READ }
Characteristic { uuid: 0000fff2-0000-1000-8000-00805f9b34fb, service_uuid: 0000d0ff-3c17-d293-8e48-14fe2e4da212, properties: WRITE }

The following GATT characteristics are used for writing requests:

• Characteristic of UUID 000033F1-0000-1000-8000-00805F9B34FB and service UUID 000055FF-0000-1000-8000-00805F9B34FB, which we will refer to as CHAR_W_01

The following GATT characteristics are used for getting response notifications:

• Characteristic of UUID 000033F2-0000-1000-8000-00805F9B34FB and service UUID 000055FF-0000-1000-8000-00805F9B34FB, which we will refer to as CHAR_N_MAIN

Note that write-characteristics (and the rest probably too...?) appear to have a limit of max. 48 bytes.

General command structure

We will distinguish between request and response commands, where the former ones are written on a certain write-characteristic and the latter ones are notified on (and thus received from) a certain notify-characteristic.

In both cases, however, the general structure is the same. The commands always start with an initial u8 ID which identifies them. Considering how GATT works, it's necessary for both requests and responses to be adequately identified.

Note that the command/field names used from now on are completely guessed, and the result of both leftover names of the RE-d app, texts from actual watch features and my own deductions of command features.

Pairing

All pairing-related request/response commands start the following way:

After that commands may contain more data.

Pairing request commands have the following structure:

This commands are written via CHAR_W_01.

Note that, without sending any key bytes or in general sending less than 4 key-bytes, the watch seems to treat the unset key bytes as 0xFF (the way to get the watch's current pair key is detailed below). Any extra bytes are ignored, but unlike with other commands, the command is accepted.

Watches may be connected to different devices without having to re-pair, as long as the pair key is the same.

The watch will prompt a dialog for the user to accept the device pairing (if no pairing exists or if pairing with a different pair key), and the following command will be received at the same time via CHAR_N_MAIN:

If the pairing dialog is accepted the following response commands will be received in order via CHAR_N_MAIN:

Furthermore, the watch may also send its current battery level via CHAR_N_MAIN after successfully pairing (battery response commands are detailed below).

If the pairing dialog is rejected instead, the following response command will be received via CHAR_N_MAIN:

However, if the watch is already paired with the requested pair key, the following response command will be received in order via CHAR_N_MAIN and nothing else will change (this way one ensures that the watch is actually paired, otherwise the dialog would prompt):

If the paired device was disconnected instead, the following response command will be received in order via CHAR_N_MAIN after pairing:

In the scenario where the watch was reset (that is, no device is paired with it), trying unk value 0x00 or any value higher or equal to 0x04 in the pairing request resulted in the watch sending the mentioned already-paired 0x1C command, but the watch did nothing and still was showing the initial instructions to pair.

The following request command may be sent via CHAR_W_01 to request the current pair key:

After sending said request command the following response command will be received via CHAR_N_MAIN:

Note that, inmediately after the initial pairing is done, sending certain command requests will make the watch display a "device successfully connected" screen. For instance, getting the watch's battery does not prompt this, but setting time/date or getting the watch's firmware (all these command requests are detailed below) does.

Furthermore, this even happens with some invalid command requests, so there might be a certain list of command IDs that are treated by the watch as the kind of commands a device will send inmediately after pairing that guarantee that the pairing was successful on both ends.

Unpairing

To unpair, send the following command request via CHAR_W_01:

Option 0x00 will reset the device (same as the reset on the watch settings, which will obviously unpair and reboot the watch). Option 0x01 appears to do the same but powering-off the watch instead of rebooting it, so that after turning it on the watch will be reset.

Requesting this command (with any of the options) when the watch is already unpaired (when it's on the initial screen) does nothing. In fact, no requests seem to do anything in this state other than the pairing request, so from now on all the command bevahior will assume that the watch is already paired with a device, with all its functionalities.

Battery

Battery request commands have the following structure:

Battery response commands have the following structure:

One may send this command request via CHAR_W_01, and the watch will send this response via CHAR_N_MAIN.

Note that, when the watch battery changes (when the percentage drops), the watch will by itself send a battery response via CHAR_N_MAIN, with the aim of notifying the device that the battery level changed.

As mentioned above, after an initial pair the watch will (only sometimes?) also send by itself a battery response via CHAR_N_MAIN.

Firmware

Firmware request commands have the following structure:

Firmware response commands have the following structure:

One may send this command request via CHAR_W_01, and the watch will send this response via CHAR_N_MAIN.

It's unclear whether firmware strings have a fixed length, but some of the app server contents for other watch models (which contain their version strings, similar to this model's ones) suggest that they may not have a fixed length.

An example of a firmware string is RH208DV000924, where V000924 corresponds to the firmware version, the same one the watch displays on the "about" menu.

Date and time

Commands to set the watch's time/date have the following structure:

Both request and response commands have the same format. One may send this command request via CHAR_W_01, and the watch will send this response via CHAR_N_MAIN. The response will be the same as the request, as some sort of confirmation that date/time were set correctly.

The watch itself computes the corresponding day of the week when displaying the date.

The watch starts by setting its date to Jan 1st 2020 and its date to 08:00:00 right after the initial pairing, and it's expected for the paired device to inmediately set the current date/time. Note that not all the available watch faces display the full date/time. In fact, the only known way of knowing the current year for the watch is viewing it on the few watch faces which actually display it.

Pulses

Pulses (pulse commands) are the way the watch sends requests to the device as responses.

Response commands sending pulses have the following structure:

The watch will send this pulse requests as responses via CHAR_N_MAIN when necessary.

The following pulse types are known:

• Value 0x02 corresponds to the user clicking the "hang call" button on a call alert message (alert messages are detailed below), telling the device to hang the current call.

• Values 0x07, 0x08 and 0x09 correspond to pausing/resuming the current music, skipping to the next song and rewinding/moving back to the previous song respectively, all user-inputs from the music menu on the watch.

• Value 0x0A corresponds to the device-finding option, where the watch "rings" the device.

Unit settings

The following command is used to set the watch's time and distance units:

This request command may be sent via CHAR_W_01, and the watch will respond with the same command (again, as some sort of confirmation) via CHAR_N_MAIN.

Note that the distance unit is only used to display the currently walked distance (either in kilometers or miles) and the time format unit is ovbiosuly used to display the current time.

Alert messages

The watch supports receiving messages from the paired device. This messages are meant to be for notifications received from the device's different messaging/social media applications, etc.

This is the currently only known request type that suffers from the max. write/command size limitation, thus alert messages have to be split into at least two request commands.

The text message is sent through various request commands of similar structure, which we will refer to as "batches".

The first request command (message batch) has the following structure:

The following (optional) message batches have the following structure:

Note that the size of each batch's message data is arbitrary, as long as all the batches end up containing the full message size sent in the first one (I guess). For instance, the RE-d app builds these batches so that no command exceeds 20 bytes in size, but as long as the commented max. size is not surpassed, longer batches/commands can be made. (maybe the app uses 20 as the command limit instead of the actual 48 because older watch hardware/software versions may have had that limit, in order to ensure compatibility with all LS02 hw/sw versions?)

After sending a message batch command request via CHAR_W_01, the following response is received via CHAR_N_MAIN (again, as some sort of confirmation):

After having split the UTF16-BE message text and sent it to the watch into all the needed batches via CHAR_W_01, the finalization command is sent via CHAR_W_01 too, essentially telling the watch that all the alert message batches are already sent:

After sending this request command, the watch will display the alert message for a short period of time (until the screen itself blocks, so the actual screen show time?), and (unless the "trash" button is clicked) the message will get logged in a "notice" list accessible from the watch menu.

After sending this finalization command request via CHAR_W_01, the following response is received via CHAR_N_MAIN (again, as some sort of confirmation):

Note that this last command shows that only batches from 0x00 to 0xFC are allowed (thus 253 max. batches, the first one and 252 other), and by the max. size write/command limitation (which leaves us with a max. text length of 22 characters for the first batch and 23 for the rest) that yields us a theoretical total max. message length of 5818 characters.

However, the watch is not really prepared to show particularly large message texts, and it appears to effectively get/use only the first 160 characters (?).

These are the supported alert message types (most of them are for different messaging/social media applications):

For alert type 0x03 surprisingly nothing happens (no notification is shown nor logged).

For alert types higher than 0x17 no notification is shown, but a message with no icon does get logged.

The call alert is a special one, where the message is likely meant to be the caller name/contact. It covers the entire screen and a button for hanging up the call is shown (pressing it will send a pulse as explained above). Even if the screen automatically locks the alert-screen persists, but pressing the call-end button will close it and sent the mentioned pulse. Actually, pressing the watch's button will also close it but won't send the pulse whatsoever (is this intended at all...?)

Weather

The watch supports displaying weather information for the current day and the following three days.

The following request command can be sent via CHAR_W_01 to set the current day's weather info:

The following request command can be sent via CHAR_W_01 to set the following days' weather info:

Note that all weather temperatures are in Celsius degrees.

These are the supported weather types:

For weather type 0x00 the watch ignores all the temperatures and sets the weather to it's default "unknown" state.

For weather types higher than 0x0E the watch displays invalid graphics data but loads temperatures fine, likely being caused by out-of-bounds memory reading of weather graphics data.

For both requests commands, the watch responds via CHAR_N_MAIN with the following command:

In fact, even for requests with invalid dates (values like 0x00, 0x03, etc.) the watch does nothing but this response command gets sent with the corresponding request date value.