Depending on how long you press the button:

* If pressed for less than three seconds:

  * If the device is not provisioned to the Matter network, it initiates the SMP server (Simple Management Protocol) and Bluetooth LE advertising for Matter commissioning.
    After that, the Device Firmware Update (DFU) over Bluetooth Low Energy can be started.
    (See `Upgrading the device firmware`_.)
    Bluetooth LE advertising makes the device discoverable over Bluetooth LE for the predefined period of time (1 hour by default).

  * If the device is already provisioned to the Matter network, it re-enables the SMP server.
    After that, the DFU over Bluetooth Low Energy can be started.
    (See `Upgrading the device firmware`_.)

* If pressed for more than three seconds, it initiates the factory reset of the device.
  Releasing the button within a 3-second window of the initiation cancels the factory reset procedure.
