serial.py

from microbit import *

# From https://support.microbit.org/support/solutions/articles/19000070728-how-to-read-the-device-serial-number
def get_serial_number():
    NRF_FICR_BASE = 0x10000000
    DEVICEID_INDEX = 25 # deviceid[1]

    @micropython.asm_thumb
    def reg_read(r0):
        ldr(r0, [r0, 0])
    return reg_read(NRF_FICR_BASE + (DEVICEID_INDEX*4));

display.scroll(get_serial_number())