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...
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.