Going to be adding Garnet SeeLevel 2 tank sensors to my fifth wheel, I messaged them and asked about integrating that with Home Assistant and they sent me their BLE Technical Documentation!!
Wonder if this could be quickly converted to an ESPHome for translation into Home Assistant.
Garnet 709BT BLE Technical Document
The Garnet 709BT hardware supports Bluetooth Low Energy (BLE), and is configured as a Broadcaster transmitting advertisement packets. It continuously cycles through its connected sensors sending out sensor data. No BLE connection is required to read the data, instead the smartphone application implements Receiver functionality to receive these packets.
When the application receives these packets it must decode the Manufacturer Specific Data to determine the Garnet Sensor Data. The first 2 bytes represent a company identifier code.
Company ID 305 Cypress Semiconductor
The following bytes represent the Garnet Sensor Data payload:
Byte 0, 1, 2 Coach ID Unique number – hardware assigned
Byte 3 Sensor Number 0-255
0 = Fresh
1 = Black
2 = Gray
3 = LPG
4 = LPG 2
5 = Galley
6 = Galley 2
7 = Temp
8 = Temp 2
9 = Temp 3
10 = Temp 4
11 = Chemical
12 = Chemical 2
13 = Battery x 10
Byte 4, 5, 6 Sensor Data ascii characters representing data value or sensor status
Byte 7, 8, 9 Sensor Volume <future>
Byte 10, 11, 12 Sensor Total <future>
Byte 13 Sensor Alarm <future>