“This project can be built in about half an hour at a cost of about $20.00 if you have existing 433Mhz or 315Mhz wireless alarm sensors.
It can also be a complete new project with wireless alarm sensors, such as infrared motion detectors and reed switches, easily and cheaply available online. Just search for 433Mhz or 315Mhz sensors that use PT2262 or EV1527 coding.
I am sure there are many people like me who have purchased a GSM/2G alarm system with wireless sensors and were happy with it, however when the 2G/GSM network was turned off where I live, I was left with an alarm system I could no longer program or even set the time on it. One day while wondering what I could do to make my alarm functional again, it occurred to me to check if an Arduino could receive signals from the sensors. I stumbled across an instuctable https://www.instructables.com/id/Decoding-and-sending-433MHz-RF-codes-with-Arduino-/ and after some experimenting determined that I could receive the signals from my existing sensors. I began the process to build an alarm system that could replace my existing alarm and would also provide increased functionality. One of the issues with the old alarm was never actually knowing exactly which of the 25 sensors went off, by adding an LCD screen to my new alarm build I now get text on the LCD indicating exactly which sensor was activated. The new alarm can still be manually armed by my existing wireless keyfobs and has a real time clock to allow it to automatically arm and disarm at preset-able times of the day.
Supplies:See additional notes at end to ensure you use the correct version of these parts.
Arduino Uno or similar
433 or 315 MHz receiver module for Arduino
DS3231 Real Time Clock module for Arduino
I2C 16x2 LDC module for Arduino
Wireless Alarm reed switches, motion sensors and remote key fobs as desired
Piezo buzzer
LED & 220 ohm resistor
Breadboard (optional but recommended)
Suitable power supply for Arduino
Jumper wires etc
PC with Arduino IDE installed
Basic knowledge of Arduino”