Use a PIR sensor, Raspberry Pi, and PiCamera to detect motion, take a timestamped photo, then send a text message alert from Gmail with Python.

motiontxt.py

# Allow less secure apps to access your Gmail account

# https://en.wikipedia.org/wiki/List_of_SMS_gateways

# 10digitNumber@mms.att.net for AT&T
# 10digitNumber@pm.sprint.com for Sprint
# 10digitNumber@tmomail.net for T-Mobile
# 10digitNumber@vzwpix.com for Verizon

from gpiozero import MotionSensor
from picamera import PiCamera
from datetime import datetime
import smtplib

camera = PiCamera()
pir = MotionSensor(4) # GPIO pin on Raspberry Pi

while True:
    pir.wait_for_motion()
    filename = datetime.now().strftime("%m-%d-%Y_%H.%M.%S.jpg")
    camera.capture(filename)
    pir.wait_for_no_motion()
    
    username = "yourAddress@gmail.com"
    password = "yourPassword"
    
    server = smtplib.SMTP("smtp.gmail.com:587")
    server.starttls()
    server.login(username, password)
    server.sendmail(username, "10digitNumber@mms.att.net", "Warning! Motion detected!")
    server.quit()