Lately, somebody started stealing from us. Took us time to figure it out. At first we thought things got lost. When they took a gas tank, it became obvious ;). As far as I know, it ain't over and it's no game. It's a lousy perimeter to defend, especially for old hippies who moved to the land of smiles because they got tired of saying "perimeter"[1].
This is a generic Arduino sketch that lets you whip up a simple and friendly alarm system from whatever sensors and controllers you've got lying around in cat-infested shoe boxes.
- A sensor (PIR motion detector, magnetic door switch, weight sensor, etc.).
- A controller (hidden button, keypad, RFID reader, etc.) to temporarily disable ("chill") the system.
- A noisy device (buzzer, ghetto-blaster, tennis ball cannon aimed at a gong, GSM modem for sending SMS, etc.).
- A LED.
- Optional "dead man switch" slave device (see below).
The early prototypes were battery powered, but doing battery replacement rounds in the mud would have been too much of a hassle, so the live systems are all AC powered (luckily, all problematic places are close to a socket). The drawback here is that one could disable the whole thing by cutting the power. The "dead man switch" trick is to have a pin that always outputs a HIGH signal sent to a slave device that should make a fuss if that signal drops. This may either be an attack or a genuine power cut (i.e. false alarm), and both may happen while I sleep, so I should wake up fast, and immediately understand we're not necessarily under attack ;). It should also be robust enough to withstand whatever took down the mother system (so that it can vow to avenge it in an extreme zoom out from above).
Does such a magical device exist? Here comes the clever bit: the relay (yellow ellipse) activates the power outlet that feeds the portable emergency lamp in our bedroom. Anything goes wrong, lights go up, and motion starts filming us getting dressed ;)
- "Chill controller" — hidden button, keypad, rfid, etc. to invoke a temporary CHILL state (1-2 minutes).
- Sensor — PIR motion sensor, magnetic door switch, weight sensor, etc.
- LED — Indicates state.
- Alarm — buzzer, piano-dropper, etc.
- [Optional] "dead man switch" slave device.
It's as simple and sleepy-user-friendly as it gets (I thank my wife for surviving the early versions without resorting to violence. Believe me. It's friendly now). There are 5 states (indicated by the LED):
READY
— LED is on: This is the normal state.WARNING
— LED blinks: Happens when the sensor gets triggered [door opened, motion detected, etc.].ALARM
— LED blinks faster, alarm goes off: Happens when aWARNING
isn't dealt with within a grace perion (a few seconds).CHILL
— LED blinks in a "hearbeat" pattern: User has activated the "chill controller" to temporarily disable the system (for 1-2 minutes), but the sensor is still getting triggered [door is open, motion is detected, etc.].COOL
— LED is off: We're in aCHILL
, and the sensor's relaxed as well.
It's simple, friendly, flexible, easy to "knit" from leftover components, and beats worrying manually ;)
[1] On the [terribly fat] chance that the burglars are reading this [or English, for that matter], consider this gist an appeal to your common sense. Don't kid yourselves this "gives you intel". Just stay away. That's the best case scenario for us as well as you. "You don't want to see me when I'm non-violent"TM.