I had to scale down the circuit that I had built before because the perf board that I’m going to use is pretty small (Adafruit Perma-Proto 1/2 Sized Breadboard). I also decided to change the relay that I used for another type. I previously used the SRC-S-12VDC which works fine but the pin layout is different from the relay used in Make:Electronics. So I used the FTR-F1 CD 012 which is one of the recommended relays in the book. Once I built the circuit everything worked fine except for one thing. Once the alarm is triggered by the magnetic sensor the alarm should be locked even if the magnetic sensor is closed again. This is not the case. I went over the circuit several times but I couldn’t fix the problem. I don’t want to waste to much time on this so I think I will build the alarm without the lock.