IoT Home Alarm: A New Beginning

Active House Alarm: Malaysian street-dogs are very territorial and alert 

Over the years I have been working on and off on my Home Alarm system, always upgrading it but never quite happy with it. I did arrive at some thoughts for a good alarm, which are:

1. It is not always ideal to catch the intruder. In the suburbs a break-in is often done by someone familiar with the neighborhood. Often he is a neighbor, a relative/friend of a neighbor who visits or house-sits. The penalty for a first offense break-in is only a few months incarceration, and after it is over, guess what, he is still your neighbor except this time he hates you. Deterrence is a better goal for a home alarm: how to convince a prospective intruder to burgle elsewhere. Even if the system gets a positive ID on the intruder, it is often better to pop a printout of the offender into his letterbox: the prospect of jail-time is is a much better deterrence.
2. The best deterrence is a concerned neighbor who investigates the alarm, sticks his head out the window, turn the light on, or somehow lets the intruder know the jig is up. He should not intervene or confront the bad guy, just the prospect of a call to the police is often enough. Of course, if your immediate neighbor is the bad guy then you have a big problem.
3. It then follows that a good alarm should have minimal false alarms: you do not want to annoy your neighbor, and worse, condition him not to investigate.
4. A successful burglary often means he will come back. He already knows the layout of the house, mode of entry, as well as the payoff.  
5. There is no such thing as a perfect alarm system. Determined intruders will always find a way in. The key goal is to convince them to go elsewhere. Like that Asics jogging shoes ad, when confronted by a lion it is sufficient just to outrun your companion. 

Asics running shoes ad

The features of a reasonably effective home alarm should then be:

1. Able to identify the intruder. This usually means high-resolution cameras with good lighting. It is a problem if he is masked, so they should also cover the driveway to identify the getaway vehicle. Ideally a light source just behind the camera should switch on. It is instinct to look at the light: you then get good face shots. There is nothing more annoying than camera footage which almost IDs the intruder. To minimize false alarms the camera should not trigger the siren. 
2. Able to raise the alarm. A siren is often enough. It should not go on for more than a few minutes: few intruders will hang around that long. The ones that do: well you probably don't want your neighbor to mess with them. Sensors that trigger the siren should be door or window switches, indoor passive infrared sensor, drawer micro-switch, etc. 
3. Notify you when offsite. This lets you review the sensors and perhaps call for help.
4. Do unexpected things. Popular commercial alarms behave in well-known, and hence predictable ways to knowledgeable intruders. Especially the sound of a snarling dog - the prospect of immediate personal injury is quite distracting. Just make sure it is not played too long. It is best not to install booby traps (paintball gun is my favorite) - they almost always catch the house occupants at some point.  

The good news is current IoT developments bring exciting new capabilities. Even inexpensive IP cameras come with motion detection and some ability to recognize humans. This is especially useful when sifting through hours and hours of security footage. Intruders often do quick surveys from  outside; so a good deterrence is posting a printout of them doing just that. A bonus is you get confirmation of online purchased deliveries. 

Smartphone Apps now allow the alarm to contact you remotely. And best of all, wireless sensors remove a major disincentive to alarm installations: expensive and often unsightly wiring. 

Best of all the IoT parts required are cheap and getting cheaper. So it is time to make a start. And a good start is a passive infrared (PIR) sensor linked directly to a siren. This way I can incrementally add to the system without needing to take it down for upgrades.

The HC-SR501 cost me only RM5 (about USD1). Note the range and delay adjustments are especially handy

The HC-SR501 PIR sensor costs only RM5 from Cytron. The HC-SR505 on the other hand was less useful as the range is a little short and not adjustable. And the price is not much different.

HC-SR501 Schematic

You can pretty much hook up the HC-SR501 directly to a siren via a relay module

The HC-SR501 can be used to directly trigger a siren. But adding an ESP8266 will let the siren be triggered by other sensors in the future. And little conveniences like alarm arm/disable functions from the smartphone.

1-channel ESP-01S Relay Module, shown with ESP8266-based ESP-01S installed

This 1-Channel ESP8266-based ESP-01S Relay Module is slightly problematic when used with an ESP-01S (see my post on this). However it can be used unmodified with the NodeMCU ESP-12E. This relay module is not to be confused with the Diymore Serial 1-channel ESP8266 Relay Module, which has an onboard CPU and is triggered from the serial port rather than a GPIO line:

Serial TTL 1-Channel ESP8266 Relay Module, with ESP-01S mounted

I found the ESP-01S a little problematic getting the GPIO lines to work as input, so for this build I used the NodeMCU ESP-12E instead:

ESP-12E NodeMCU development board, with CH340 USB interface

Wiring Diagram

The wiring is, from the point of view of the ESP-12E:

GPIO13 - Relay control line

GPIO12 - PIR output

The assembled system looks like this:

Left to right: USB power connector, NodeMCU ESP-12E, 1-channel ESP8266 Relay Module and HC-SR501 PIR sensor

You connect your siren to the relay contacts. This lets you switch most sirens, from mains powered sirens, 12V automotive car horns or a more discreet 5V buzzer. Personally, I find the 12V automotive siren plenty loud and easy to back up with car batteries.

12V Siren

As usual there is a sample program in github.  The program creates a WiFi access point, "SirenAccessPoint". and you log into it using your smartphone. You then type into your favorite browser:

http://192.168.4.1/arm           to turn the alarm on

http://192.168.4.1/disable      to turn the alarm off

http://192.168.4.1/sirenon      to turn the siren on

http://192.168.4.1/sirenoff     to turn the siren off

As a start the system does not assume you have a WiFi infrastructure, and you can pretty much move it to any location you want to protect. One caveat is many PIR sensors are triggered by direct sunlight, so your mileage will vary.

By having other devices to log into the AP, we can now trigger, disarm or mute the siren using the same http messages. However a true IoT system needs a way to contact your smartphone offsite. For that we will be needing some kind of communications infrastructure, usually an MQTT gateway. For simplicity, later iterations of this project will use WiFi broadband, as with the other IoT projects in this blog.

There are many things to add: door magnetic switches, IP cameras, motion detectors and lighting control. But there you have it: a cheap DIY House Alarm to start you off. 

Nightwatch

In the meantime, I have a pair of rescued Malaysian street-dogs on duty round the clock, and honestly, that IoT Alarm System has a lot to live up to.

Happy trails.