Building a High Tech Alarm System with Raspberry Pi

Second Edition

 

 

Have you seen “Mission Impossible” with Tom Cruise? Would you like to know how to catch him with a $40.00 sensor? Then this book is for you.

This book will guide you through the building and test of a ten zone alarm system. In addition to building the hardware, we will also cover the code which runs on the Raspberry Pi. The code currently ‘speaks’ and writes English, but by following the directions in the code chapter you can easily make it speak French, Spanish, German or Dutch.

In this book we will discuss the basic components of any alarm system. All alarm systems have two basic functions. First, they monitor their environment looking for a change such as a door or window opening or someone moving about in the room. The second function of the system is to alert the human to this change. Our alarm system uses a scanning type software to detect intruders.

We will use the ‘standard’ guard dog as an analogy. In a scanned type of system, the guard dog paces back and forth at the fence looking out for either an intruder or someone that it recognizes. In our design, if you have an alarm key, you can disarm the system and enter. In an interrupt driven system, the dog is asleep until it hears an intruder (or you). It then wakes up and deals with the situation. I have chosen the scanning method because in my opinion the software is easier to write and explain. It can scan all ten zones in about one second.

 You don’t have to be an electrical engineer to install an alarm system, just a good carpenter, painter, and plasterer! I’m not by the way so I’ll leave hiding wires up to you.

Also, because our alarm system runs on 12 volts, you don’t have to be a licensed electrician to install it. If you can plug in a wall adapter, you can build and test this alarm system.

 In this book we will discuss how to plan an alarm system for your home and business. This chapter is provided for educational purposes only and should not be considered installation instructions for the alarm system described in this book. This is because no two houses or businesses are the same. What I am describing here is a typical installation.

 There are two basic types of alarm systems: wired and wireless.

 The wireless system is quick and easy to install. It is however easy for a professional burglar to jam the wireless signal that controls the alarm. There are numerous YouTube videos on the subject and the equipment required to carry out the attack costs less than $50USD on Amazon. For about twice that amount you can purchase a device capable of also jamming the cellular signal, so that the panel cannot contact the alarm company to tell them that it has been jammed.

 The cost of a wired alarm system is considerably more up front. This is due to the labor involved in fishing wires thru walls and drilling holes to mount the sensors. The upside to a wired system is that there is no wireless alarm signal to jam. It is of course still possible to jam the cellular system or cut the phone line. That is why loud sirens were invented.

 Our system is not monitored by an alarm system company so there is no one for the panel to call. Also, SMS messaging system protocols and frequencies vary from country to country. For that reason, an SMS option was not included in the design. I should point out that while this is a fun and educational project, there is no substitute for a live monitored professional alarm system. If you are protecting elderly or infirmed persons or a store that sells high end merchandise, then I would suggest that a live monitored wired system is the way to go. It is true that phone lines can be cut, and cellular links can be jammed, but a 110dBm siren will at the very least alert the neighbors and hopefully scare off a would-be thief. It might be advisable to tell your neighbors about your new alarm system and apologize in advance for any false alarms.

 One other, somewhat controversial topic is stickers on your window that say “Protected by Acme Alarm Company”. In my opinion, the sticker will deter the casual or amateur burglar and tell the pro what frequency to jam.

 Planning is by far the most important part of the installation. Poor planning has caused more headaches than any other part of an alarm system installation project.

 

Step 1 – The Walk-about

 

As the name suggests, take a walk around the property you will be protecting, both inside and out. Try to think like a bad guy.

Ask yourself “If I wanted to break into this house / office / warehouse, how would I do it?”

Take pictures if you think it will help. Make sketches of the inside and outside of the building so that you can plan where you are going to put your sensors. There are several free CAD programs that will help you with this.

Here is a simple check list for you:

 

·         How many doors are there?

·         What type of doors are they? Garage doors? Human entry doors? Pet doors? (Seriously burglars have used children)

·         How many windows are there? How many open?

·         How many windows on the ground floor and how many on the second floor? (Burglars use portable ladders)

·         Is there a hedge or a privacy fence. (Burglars love cedar hedges and privacy fences.)

·         Once the burglar is inside, where can they go from there? (Main hallway, kitchen door, patio door)

·         How many rooms are there that you will have to protect?

·         Is everything on the same floor or is there more than one floor.

·         What about special alarms? Panic alarm in the bedroom? Smoke alarm in the kitchen? Flood alarm in the basement? Heat detector in the garage?

Table of Contents:

 

Chapter 1:

 

In chapter 1 we discuss the basic components of most alarm systems. From simple door and window contacts to more sophisticated sensors like Passive Infra-Red (PIR) motion sensors. (Remember Tom Cruise and the $40.00 sensor?) In addition to the eight alarm zones there are two Fire Zones. These zones are connected to heat rise or smoke detectors. These zones are designed to alert the human of a fire, even if the system is disarmed.

 

Chapter 2

 

In chapter 2 we learn how the hardware that is connected to the sensors works. How does the hardware detect motion or a door or window opening? How does the hardware detect a cut alarm system wire? How does the system detect a shorted sensor?

 

Chapter 3

 

Chapter 3 is about the ‘Human Interface’. In this chapter we discuss how the system interacts with the outside world. System messages such as “System Armed” are sent to a two line liquid crystal display. The system also talks to the world using the stereo speakers attached to the Raspberry Pi. As I said before, the default language is English. This can be changed to French, Spanish, German or Dutch by the system designer. An alarm key or optional RFID card reader can be used to arm or disarm the system.

 

Chapter 4

 

Chapter 4 describes the software in detail. The software has a two minute entry and exit delay via zone 1. The latest version of the software allows for a USB video camera to be connected to the alarm system. The Motion software package also includes motion detection and video capture.

 

Chapter 5

 

Chapter covers the assembly of the main printed circuit board of the alarm system. Thru hole parts are used thru out the design so advanced soldering skills are not required.

 

Chapter 6

 

In chapter 6 we construct and test the harnesses which connect the human interfaces to the alarm system. Details of how the PIR motion sensors, door/window contacts are connected to the system. What the heck is an ‘end of line resistor’ and what does it do? The alarm system board is tested using push button switches.

  

Chapter 7

 

Chapter 7 describes four typical scenarios. The planning of an alarm system to protect a two story, four bedroom house; a restaurant or pub; an office space and a laboratory. These are ‘typical scenarios’ because no two installations are the same.

 

Chapter 8

 

This chapter describes some future enhancements to the system for more advanced users. Other sensors which can be used with the alarm system are described in detail. Instructions for running the alarm system “headless” (No keyboard, monitor or mouse required.) are also provided.

 

Chapter 9

 

This chapter describes in detail an expansion board which can be built and attached to an existing alarm system board. The expansion board uses I2C technology to communicate with the alarm panel. The system is capable of addressing up to six expansion boards. Each expansion board has eight inputs and eight outputs. The alarm inputs on the expansion board are identical to the ones on the main board. The eight outputs are solid state relays capable of sinking two amperes at twenty four volts or forty eight watts.

 

It is my hope that you will enjoy reading this book as much as I enjoyed writing it.

 

 

Author Bio:

William (Bill) Pretty

Bill began his career in electronics in the early 80’s with a small telecom startup company that would eventually become a large multinational. He left there to pursue a career in commercial aviation in Canada’s north.  From there he joined the Ontario Center for Microelectronics, a provincially funded research and development center. Bill left there for a career in the military as a civilian contractor at what was then called Defense Research Establishment Ottawa. That began a career which was to span over 30 years.

Over the years Bill has acquired extensive knowledge in the field of technical security and started his own company in 2010. That company was called William Pretty Security Inc. and provided support in the form of research and development, to various law enforcement and private security agencies.

In 2014 he retired to pursue a career in writing. He has several books for sale on Amazon, for the electronics hobbyist.