How to emit GObject signal once?

Question

First, I have less than one year experience with Python. I normally have problems with data usage with my ISP such that I discover late that I have overused my data allocation. So, in order to evade this problem, I thought of creating a script that would run immediately I tether my phone to my PC. The script scrapes data from my ISP's website and returns my data bundle balance.

I found out that pyudev is useful in such an instance where I would like to constantly monitor my usb ports activities. Part of the script is as shown below. The problem is identify_phone is called 3 times (from my experience) which tends to call the scraping method 3 times whereas I would like it to be called once. I tried using the global value but it does not work as expected. I have searched online but there are scarce resources on pyudev.

Any help would be appreciated (Including any revision on my code :P)

import glib
import re
import subprocess
import requests
import bs4
import datetime
import sys
from selenium import webdriver

from pyudev import Context, Monitor

def identify_phone(observer, device):
    global last_updated
    current_time = datetime.datetime.now()
    time_diff = current_time - last_updated

    if time_diff.seconds < 10:#300:
        pass
    else:
        #print('\Checking USB ports...')
        try:
            tout = subprocess.check_output("lsusb | grep 1234:1234", shell=True) #check if specific usb device (phone) is connected
        except subprocess.CalledProcessError:
            tout = None
        if tout is not None: 
            device_found = True
        else:
            device_found = False
        last_updated = datetime.datetime.now()

        get_network_data()# scrapes ISP website

try:
    device_found = False
    last_updated = datetime.datetime.now()
    try:
        from pyudev.glib import MonitorObserver

    except ImportError:
        from pyudev.glib import GUDevMonitorObserver as MonitorObserver

    context = Context()
    monitor = Monitor.from_netlink(context)

    monitor.filter_by(subsystem='usb')
    observer = MonitorObserver(monitor)

    observer.connect('device-added', identify_phone)
    monitor.start()

    glib.MainLoop().run()

except KeyboardInterrupt:
    print('\nShutdown requested.\nExiting gracefully...')
    sys.exit(0)