I bought these cheap door chime/alarm gadgets at Harbor freight initially because I wanted the door switch and the alarm. The problem is, though, that the alarm squeals as soon as the door is open, which doesn't give me a chance to disarm it.
My ultimate goal is to control the alarm with an ESP8266. For now I'm just going to show you how I altered the gadget.
Step 1: Crack It Open.
Take the batteries out, and there is a screw that holds the case together. This is the only screw holding it together.
Step 2: Connecting Signals
I Cut the trace that connects the upper end of the reed switch to the IC. I soldered a wire (I used a piece of cat6 and cut off all of the white wires, but I would have used standard 4 conductor phone wire if I had some laying around) I soldered the blue wire to the switch. Next, I soldered the brown wire to pin 4 on the IC.
Step 3: Power Connections
I disconnected the red power wire from the positive battery terminal and inserted a rectifier diode. My plan is to use the batteries for backup in case of a power failure. I also connected the orange wire from the cat6 to the cathode side of the diode.
I soldered the green wire to the negative battery post to provide common ground.
Step 4: Testing:
I connected the ground to the ground of my prototype board, with my ESP8266-12 already on board. I connected the blue to a GPIO programmed as a pullup input, and the brown to another as an output.
Setting the output to high causes the alarm to sound. Pulling the magnet away causes the input to go high.
Step 5: Final Comments
I haven't had time to sit down and write the firmware, but when complete it will have peer-to-peer communication with another identical device (front door and back door) so it will sound both simultaneously. It will have the capability to send me and my Bride a text message when the alarm has been triggered. We will be able to arm/disarm via internet, so we can disarm via smartphone from the car.
I thought I would go ahead and publish this portion now, because I am sure there's something else I haven't thought of that I can include, so I will be checking the comments. I plan to hardwire the switch to alarm when I complete testing, and likely include a third peer somewhere in the home that just blares a horn.