Home Security

A few years ago, when we started on the home renovation project, I installed an alarm system.  It’s got sensors in several rooms, switches on some doors, a keypad by the door for arming and disarming and a loud bell on the wall outside.  Occasionally someone comes in and forgets the code but on the whole it works.

 

There are a couple of things that became obvious to me while I set it up:

• It’s really simple – it’s clearly nothing more than a cheap microcontroller and some fairly simple software to ring a bell if a circuit gets broken.
• It’s not very useful – having the blinking light on the box outside might deter the casual thief but if someone actually does break in all it can do is ring a bell and annoy the neighbours.

So let’s build a better one.

Ideally one that:

• Tells us if someone breaks in – no matter where we are.
• Give us a chance to cancel a false alarm before it starts to annoy the neighbours.
• Lets us set and unset it from our phones
• Send us a message if someone goes out without closing all the doors (instead of displaying a cryptic message on an LCD and a slightly different pattern of beeps).
• Will arm itself if everyone goes out without remembering to do it.
• Has a night mode that doesn’t wake everyone up when it’s set and unset.
• Will run for a few days without mains electricity.
• Doesn’t completely rely on my home internet connection.

Looking around on the internet there are a few projects which will allow you to hook up a few switches to something that sends you a message – but nothing that does all the above or works as a drop in replacement for a the existing system.  If you know of anything please let me know.

Right now my plans revolve around a raspberry pi hooked up via the I2C or SPI bus to a few ADCs that can measure the resistance of the sensor circuits.
Twitter, email or sms messages can be sent & received via my home internet connection. A 3G USB stick can act as a backup internet connection.
The existing alarm runs off a 12v lead-acid battery when the power fails so the new one can do the same.

One more thing – it has to have some way to control it if all our phones are flat and there’s no internet connectivity or mains electricity.  This means it has to have some sort of keypad that everyone can use. I can’t find anything that easily plugs into a raspberry pi via 10m of alarm wire and looks good enough to permanently install next to the front door. Ideally I could re-use the existing one but I have no idea how to interface to it.