A door alarm for my house and garage.

December 26th, 2009

If you’ve looked about my sites you’ll know I make things. Lots of things. This means spending lots of time in the garage. Often I am dashing about between house and garage as I am busy making stuff. My house actually has two garages, an old on on one side of the house and my new, double garage on the other. It is in the new garage I have all my tools work on most projects.

housegarage My house and separate garage.

One thing that always worries me about being in the garage is making sure no one goes into the house (and vice-versa). Locking the doors each time I go from one to the other quickly becomes annoying so instead I decided to make a little door alarm. Basically, when I am in the garage, an alarm sounds if someone opens the front door of the house and, when I am in the house, an alarm sounds when someone opens the door to the garage.

To build this I used two small boxes, some magnetic reed switches, some switches and LEDs (with current limiting resistors), a six volt power supply and four wires of the data cable I had run between the house and garage when I had it built.

alarmcircuit Circuit diagram.

The circuit is really simple. Everything on the left is in the house, everything on the right in the garage. Basically each little box contains a toggle switch, an LED to indicate the alarm is on, a buzzer and a magnetic reed switch attached to the door.

The alarm works by sounding a buzzer when the opposite door is open. So if you are in the house and have the alarm switched on the buzzer in the house sounds if someone opens the garage door. If you are in the garage and the alarm is on the buzzer in there sounds if the house door is opened.  The toggle switch on each box turns off it’s buzzer (say you are in the house and you know the garage door is open and don’t want it buzzing). The LED just shows the alarm is on and will buzz when the opposite door is open. The reed switches are wired so that the switch is open when the magnet is in place. The reed switch itself is attached to the door frame and the magnets are on the door. When the door opens the switch closes and the alarm sounds.

The power supply is an old 6 volt wall plug I had lying about. To completely turn off the the alarm I simply pull out the power supply lead.

wiring Garage alarm box showing wiring and reed switch.

garagealarm Garage alarm box (the power was off so the LED isn’t glowing).

insidealarm House alarm box next to normal home alarm.

Now I can work in either the garage or house and leave the doors unlocked (but closed) and know that if anyone opens a door I will hear it where ever I am.

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