Intro: Simple Magnetic Alarm
Wary of intruders in the night? Don't feel secure knowing that there are expert lockpickers prowling the neighborhood? Perhaps you live in an apartment and you don't trust the landlord because he seems to watch you? Well here's a simple solution for your problems (at least in your room).
I apologize for the crappy photos and for the fact that I kind of broke my smoke detector's alarm so until I find the other one that is wandering around the house somewhere, I have created this temporary set-up to give you all the plans on how to create this alarm.
1. Disc magnet
2. Small flashlight
3. Alarm (old smoke detector, alarm clock, etc.)
4. Metal right angle (or plate)
6. Conductive foil
7. 9v battery
8. Electrician's tape
9. 9v clip (optional, but easier)
10. Capacitor (optional unless you need it)
Step 1: Only the Beginning...
Ok, confession time. I broke my smoke detector's alarm, so I am unable to show it to you correctly (though I did salvage parts for other projects). Hopefully you understood the intro photos in how this works. So I'm showing it using an old speaker (which I'm converting later, so I didn't mind cutting the wires).
1. Cut the wires to your alarm (or solder some on, if neccessary) and strip the ends.
2. Take the cover off of your flashlight and keep only the plastic lens holder (don't keep the lens)
3. Put your disc magnet into the plastic housing. Should have enough room to move freely, but not enough to slide or flip around.
4. Now take your 9v battery and put a piece of electrican's tape on it.
Step 2: This Is the End of the Instructable.
1. Take a piece of wire and tape it (or use the 9v clip and twist the wires together) to the negative terminal of the battery. Attach the other end to the middle of the battery on the electrician's tape (I taped the tip down, you can glue it).
2. Now take the negative wire coming from the alarm and place it in the middle of the battery on the electrician's tape, but not touching the other wire.
3. Take the postive wire from the alarm and attach it to positive battery terminal (or clip)
4. Place the metal plate (or right angle) on top of the magnet inside the housing. Put the housing over the wires on the battery and tape the housing to the battery. Now you have a primed alarm.
Some other ideas that I didn't include in this instructable:
1. Drill a small hole through the center of the magnet and thread some string in and tie a knot on the other side. Now you have an easy reset string.
2. Install a hidden on/off button somewhere so you can set up the alarm easy.
If you have any improvement ideas, I'd be glad to hear them...
Step 3: Smoke Alarm's Design (I Found the Other One)
More or less the pictures below will be your guide. The smoke detector you use may be set up differently, but the way to figure out which points to solder is the same. You'll need a multimeter to test between the points or some electric wire.
1. Hook the circuit board up to the 9v battery.
2. Using the multimeter/wire, test which points react to others.
3. After several tests, you should have figured out that two of the points underneath the detector (located right next to each other) will allow you to by-pass the detector.
4. Unhook the battery and just use some solder to connect these two points together.
Now you have an alarm to hook into your system. Good Job...