BT Inspector for Flipper Zero

A BLE scanner and GATT explorer for the Flipper Zero, in the spirit of BTInspector for iOS: discover nearby Bluetooth Low Energy devices, see their signal strength and everything they broadcast, then connect and inspect their services and characteristics: read, write, subscribe, and log it all.

Read this first. This app cannot run on stock Flipper firmware. The Flipper's radio coprocessor ships with ST's "BLE Light" stack, which can only advertise (peripheral role). It cannot scan for or connect to other devices. BT Inspector is therefore delivered as a custom firmware build that swaps in ST's full BLE stack and exports the BLE command API to apps. The app itself is a normal .fap. build.sh does all of this. See Why a custom firmware build.

Features

• Live scan list. Every BLE advertiser in range, sorted by RSSI, refreshed every 300 ms as you move around. Shows name (or "(no name)"), RSSI in dBm with signal bars, address and vendor. Devices unseen for 60 s drop off.
• Device page. Address and address type, current/best RSSI and packet count, advertising type (connectable or not), flags, advertised service UUIDs (16/32/128-bit, named when known), service data, Tx power, appearance, manufacturer data and raw advertisement / scan-response bytes. Updates live.
• Identification. Manufacturer IDs map to vendor names. Decoders for:
  • Apple Continuity: iBeacon (UUID/major/minor/Tx), Proximity Pairing with AirPods/Beats model name and left / right / case battery and charging state, Nearby Info (device activity), Nearby Action, Find My, AirDrop, Handoff, AirPlay, tethering.
  • Microsoft Connected Devices beacon: device type (Windows desktop/laptop, Xbox, Surface Hub, Android, iPhone, ...).
  • Google Fast Pair model ID, Eddystone UID/URL/TLM (URL decoded), COVID Exposure Notification.
• Connect and interrogate. OK on a connectable device connects (MTU is negotiated), discovers all primary services, then characteristics with their properties (Read, Write, write-without-response, Notify, Indicate, Broadcast).
• Read device info (first item in the service list): reads every readable characteristic of the Generic Access, Device Information and Battery services in one go: device name, appearance, model number, serial number, firmware / hardware / software revision, manufacturer name, PnP ID, battery level.
• Characteristic page. Read any characteristic, including custom 128-bit ones. Values are shown as hex plus decoded forms: printable string, u8/i8, u16, u32, and SIG-specific formats (battery %, appearance, preferred connection parameters, PnP ID, heart rate, temperature, humidity, pressure, Tx power, date/time). Long values are fetched with read-long.
• Write a value back as text, hex bytes or a number (little-endian, sized to the current value or the magnitude). Uses write-with-response when the characteristic supports it, otherwise write-without-response. A readable characteristic is re-read after a write.
• Subscribe to notifications / indications (the CCCD is located automatically). Incoming values update the page and the history.
• Value history. Each value seen for the open characteristic (reads and notifications) is kept with a timestamp, newest first.
• Session log. Every event is written with a date/time stamp to SD:/apps_data/bt_inspector/bti_YYYYMMDD_HHMMSS.log: devices found (and renamed), connects, services, characteristics, reads, writes, notifications, errors. Copy it off the SD card (or via qFlipper) for analysis.

Building and installing

Requirements: Linux or macOS with git, python3 and a few GB of disk. The firmware build system downloads its own ARM toolchain.

./build.sh          # clone firmware 1.4.3, export the BLE API, build firmware + .fap
./build.sh flash    # same, then flash over USB (Flipper connected, qFlipper closed)
./build.sh fap      # rebuild only the .fap after editing the app

Options via environment variables: FW_TAG (firmware tag, default 1.4.3), FW_DIR (where to clone), JOBS (parallel compile jobs, default 4), BLE_API (which ST API to export, see below).

The result is a standard update package in flipperzero-firmware/dist/f7-C/f7-update-local/. It contains the firmware, the full radio stack, and the app as apps/Bluetooth/bt_inspector.fap in its resources. To install without USB flashing, copy that folder to the SD card (for example SD:/update/) and open it in the Flipper's file browser. Installing an official firmware later restores the light stack the same way.

The .fap alone is at flipperzero-firmware/build/f7-firmware-C/.extapps/; after the firmware is installed once, app updates are just a file copy to SD:/apps/Bluetooth/. It only loads on this firmware (API version 87.2 with the exported symbols); the stock loader rejects it with an API mismatch.

To build the app with ufbt instead of the firmware tree, point ufbt at the SDK the build produces:

ufbt update --local=flipperzero-firmware/dist/f7-C/flipper-z-f7-sdk-local.zip
cd bt_inspector && ufbt        # -> dist/bt_inspector.fap ; `ufbt launch` installs it

The first build takes 5-15 minutes; later builds are incremental.

Using the app

BT Inspector appears in the Flipper's main menu. While it runs, the Flipper's own BLE advertising is stopped (and any phone connection dropped); it is restored on exit.

Screen	Up / Down	OK	Left	Right	Back
Scan list	select device	device page			exit app
Device page	scroll	Connect (if connectable)			scan list
Services	select	open service / read device info			disconnect, device page
Characteristics	select	open characteristic (auto-read)			services
Characteristic	scroll	Read	Notify / Unsub	Write	characteristics
Write menu	select	Text / Hex bytes / Number			characteristic

Status messages ("Read OK (5 B)", "Write failed: Write not permitted", "Notifications on", ...) appear on the characteristic page.

On stock firmware the app opens with an explanation instead of scanning.

Log format

One event per line:

[2026-09-11 09:12:03] START stack=full advertising_was=1
[2026-09-11 09:12:04] DEVICE 5C:F3:70:9A:11:20 ADV_IND rssi=-58 name="Living Room" vendor=Apple adv=02 01 1A 0B FF 4C 00 ...
[2026-09-11 09:12:20] CONNECTING Living Room
[2026-09-11 09:12:21] CONNECTED Living Room mtu=247
[2026-09-11 09:12:21] SERVICE 180A Device Information handles 0x0010-0x001C
[2026-09-11 09:12:25] CHAR 2A26 handle 0x0016 props 0x02
[2026-09-11 09:12:26] READ 0x0016 = 31 2E 32 2E 30
[2026-09-11 09:12:40] WRITE 0x0021 = 01
[2026-09-11 09:12:41] NOTIFY 0x0024 = 64
[2026-09-11 09:13:00] DISCONNECT

A DEVICE line is written when a device is first seen and again when its name changes. INFO lines come from "Read device info".

Why a custom firmware build

Three facts about the Flipper Zero drive the design:

1. The STM32WB55's second core runs a prebuilt ST BLE stack. Flipper ships stm32wb5x_BLE_Stack_light_fw.bin (peripheral + broadcaster only). ST's stm32wb5x_BLE_Stack_full_fw.bin adds observer and central roles. The firmware build system already supports it (COPRO_STACK_TYPE=ble_full) and the firmware recognises it at runtime (FuriHalBtStackFull).

2. External .fap apps can only call functions listed in the firmware's API table. The ST aci_* / hci_* command functions are not in it, so a stock .fap cannot start a scan or a connection. build.sh adds ST's command headers to the SDK (lib/stm32wb.scons), adds extern "C" guards to them (the API table is C++), lets fbt regenerate api_symbols.csv, and enables the selected functions. The API minor version becomes 87.2.

3. Every exported function is kept in the firmware image, so BLE_API trades generality for flash. The full stack loads at 0x080CE000 (light: 0x080D7000); the space between the firmware and the stack is the Flipper's internal storage:

   BLE_API	exported	firmware	pages left, full stack	pages left, extended stack
   min (app's own 15 imports)	15	770 KB	18	9
   hci,gatt (default)	127	779 KB	15	6
   all	211	~788 KB	13	4
   stock light-stack firmware	0	768 KB	27	n/a

   Any comma list of hci,gap,gatt,hal,l2cap works. extended refers to stm32wb5x_BLE_Stack_full_extended_fw.bin (BLE 5 extended advertising, Coded PHY), which loads at 0x080C5000; it is not selected by this script.

Extra firmware APIs exported to apps

Beyond the ST BLE commands, build.sh enables a set of firmware functions that stock firmware keeps internal, so any .fap on this firmware can use them. The set is a list of name patterns in build.sh (EXPORT_ENABLE); each enabled symbol costs one API-table entry.

• BLE peripheral internals (gap_*, safe ble_glue_*, furi_hal_bt_init): drive GAP directly, run a custom GATT server, change the advertised name and the extra-beacon config, read connection state and radio-stack status, without going through the firmware's serial profile. The coprocessor firmware-update calls (ble_glue_fus_stack_delete/install) are deliberately left disabled, since they can erase the radio stack.

build.sh also widens the GAP roles the firmware initialises (GAP_PERIPHERAL_ROLE | GAP_CENTRAL_ROLE | GAP_OBSERVER_ROLE) in targets/f7/ble_glue/gap.c. The app itself uses HCI-level scan and connect commands, so this is belt-and-braces.

How it works

bt_inspector.c   UI (ViewDispatcher: scan list, text page, menus, inputs),
                 worker thread for blocking BLE operations, session log
ble_central.c    scan / connect / GATT client on top of the ST stack.
                 Registers a handler with the firmware's BLE event dispatcher,
                 acknowledges its own events (advertising reports, our
                 connection's events) so the firmware's peripheral GAP never
                 sees them, and turns async ATT events into synchronous calls
ble_names.c      vendor / UUID / appearance tables and value decoders

The app registers for BLE events, stops the Flipper's own advertising, then issues hci_le_set_scan_*, hci_le_create_connection and aci_gatt_* commands directly. Connection-complete events are distinguished from the firmware's peripheral connections by the role field. Advertising reports are parsed from the raw HCI payload (the ST header's Advertising_Report_t is not a wire overlay).

Limitations

• BLE only. The STM32WB55 has no Bluetooth Classic (BR/EDR), so classic devices cannot be seen from any Flipper.
• Apple battery levels come from what AirPods/Beats broadcast. Battery of iPhones/Macs is only exposed to paired Apple devices.
• Vendor, UUID and Apple model tables are curated subsets; unknown IDs are shown as hex. Apple Continuity layouts are community-documented and may drift.
• Value history is kept for the open characteristic; the log file has all of it.
• iOS-only BTInspector features (Shortcuts, Live Activities, background scanning mapped by location) have no Flipper equivalent.
• Pairing/bonding with the target is not implemented; characteristics that require encryption report "Insufficient auth" / "Insufficient encryption".
• Tested by compiling into firmware 1.4.3; on-device behaviour needs a Flipper with the full stack installed.

Troubleshooting

• "Radio stack has no scanning" on launch: the light stack is installed. Install the package produced by build.sh, which includes radio.bin with the full stack.
• Build killed / out of memory: JOBS=2 ./build.sh.
• App refuses to load ("API mismatch" / unresolved symbol): the firmware on the device is not the one from build.sh, or it was built with a smaller BLE_API than the app needs. Reinstall the update package.
• "API version is still WIP" during a build: fbt found symbols the script did not classify. Open targets/f7/api_symbols.csv, replace the remaining ? marks with + or -, rerun.
• Connect failed: Timeout: the device may not be connectable (see the advertising type on the device page), or it is out of range. Random-address devices that rotate their address may need re-selecting from the list.

Layout

bt_inspector/      app sources, application.fam, icon.png
build.sh           firmware build / flash script
flipperzero-firmware/   created by build.sh (git-ignored)