Bluetooth Device Inspector

How to inspect a Bluetooth device

1. Turn Bluetooth on and wake the device: put on the heart-rate strap, press a button on the sensor, or open the pairing mode described in its manual.
2. Press Scan for a device. The browser opens its own chooser listing nearby Bluetooth Low Energy (BLE) devices. Select yours and press Pair or Connect.
3. The tool connects and lists every accessible service with its characteristics: Characteristic (name and UUID), Properties and Value.
4. Press Read on one characteristic, or Read all values to read every readable one at once.
5. For characteristics marked notify or indicate, press Subscribe. Each new value is shown in the table and added to the Notifications log with a timestamp, so you can watch a heart rate or a sensor change live.
6. Press Disconnect when you are done, or simply close the page.

You don’t need to pair the device in your system settings first: the browser handles the connection itself, and only for this page.

Services, characteristics and UUIDs

A BLE device exposes its data through GATT (Generic Attribute Profile). Data is grouped into services, such as Battery (0x180F) or Heart Rate (0x180D), and each service holds characteristics, such as Battery Level (0x2A19) or Heart Rate Measurement (0x2A37). Standard ones defined by the Bluetooth SIG have a short 16-bit UUID, which this tool shows as 0x2A19 with its official name. Manufacturer-specific ones use a full 128-bit UUID and are shown as Unknown service or Unknown characteristic, except for common serial services such as Nordic UART and HM-10.

The Properties say what you can do with a characteristic: read (the value can be read on demand), write and write w/o response (the app can send data), notify and indicate (the device pushes new values; an indication is also acknowledged).

Reading the values

Each value is shown three ways when possible:

• a decoded value for well-known characteristics: battery level in %, heart rate in bpm, temperature in °C (0.01 °C steps), humidity in %, pressure in hPa, Tx power in dBm, appearance category, PnP vendor and product IDs, and thermometer readings in IEEE-11073 FLOAT format;
• the text in quotes when the bytes are readable UTF-8, as for the device name, manufacturer, model or firmware revision;
• the raw hex bytes, always.

Multi-byte numbers in GATT are little-endian: 0A 09 in a Temperature characteristic is 0x090A = 2314, i.e. 23.14 °C.

What the browser allows

Web Bluetooth only lets a page use the services it asked for in advance. This tool asks for the standard services (Generic Access, Device Information, Battery, Heart Rate, Health Thermometer, Environmental Sensing, Cycling, Running, Weight Scale, Fitness Machine and more) plus Nordic UART and HM-10. Chrome also blocks some sensitive services and characteristics, such as HID (keyboards and mice) and serial numbers; those show Blocked by the browser or are left out. Classic Bluetooth devices such as headphones and speakers are not BLE and can’t be inspected.