Intro: Hack a Wireless Doorbell Into a Wireless Alarm Switch or On/off Switch
I recently built an alarm system and installed it in my house. I used magnetic switches on the doors and hardwired them through the attic.The windows were another story and hard wiring them wasn't an option. I needed a wireless solution and this is what I came up with thanks to some helpful tips from the guys at www.dutchforce.com
Step 1: Required Parts and Components
(1) wireless doorbell kit (get the one with the longest range that you can find with a button and the receiver)
(1) npn 2n2222 transistor (any small signal npn transistor should work)
(1) magnetic NO (normally open) alarm switch
(1) roll of double sided tape.
shrink wrap or electrical tape
3mm drill (bigger is ok, it's just for running wires trough the cases)
24 guage wire ( approximately 2' (60 cm))
soldering iron and solder
Step 2: Prepping the Receiver
1. Start by removing the back of the doorbell receiver. That is the part without the button.
2. locate the small speaker. It should have two wires running to it.
3. Solder a 3" (8cm) wire to each of the terminals on the speaker if you want to keep the chime noise. If not just unsolder the existing wires from the speaker and use them.
4. The 2n2222 transistor is set up like this. Solder one of the wires from the speaker to the emitter leg of the transistor and the other wire to the base leg of the transistor. Attach a 12" (30cm) piece of wire to the base leg and a 12" (30cm) piece of wire to the collector leg of the transistor.
5. Use shrink wrap or electrical tape on all of those joints so that they don't touch each other and short out.
6. Drill a small hole in the case and run the two 12" (30cm) wires out through the hole. The 12" (30cm) wire from the transistor base is you negative or ground connection. The 12" wire from the collector leg of the transistor is the positive connection. I ran mine through the mounting hole since I won't be using it.
7. Put this aside for now and move on to the button prep.
Step 3: Prepping the Button
You now are the proud owner of a great wireless momentary switch. You can make it into a latching on/off switch for use with many different items by adding the simple flip-flop circuit shown in the photos.
To use it as a wireless alarm switch for your security system though we will have to complete a few more steps.
1. Locate the button part of your wireless doorbell. Open the case (varies for different brands) and find the small tactile button located on it.
2. You can check with a continuity tester to be sure it is a NO (normally open) switch which means that if you press it, it will allow current to flow (or make your continuity tester beep or light up). If you release it, it should open and stop the current from flowing.
3. Drill a small hole in the side of the button case or housing. To make it easier on myself, I removed the remaining plastic from the hole area and made it into a notch. Thread the wire from the magnetic alarm switch through this hole (if you left it as a hole) and to the momentary tactile switch. Cut the wire and strip it so that it can be soldered to the momentary switch poles. Remove the circuit board from the case and locate the momentary switch terminals on the solder side of the board. Some tactile switches, like the ones shown, have four poles. There are still only two that you can use as the poles are connected to each other. on either side. I made this one for a double window, so I used a magnetic switch on each side. Either window will trip the alarm.
4. Solder one of the wires from the magnetic switch to one of the terminals of the momentary tactile switch and the other wire to the other terminal. It doesn't matter which wire goes to which terminal as long as they are not two of the terminals that are connected within the switch.
5. Test your soldering by putting the magnetic side of the magnetic switch next to the side you just soldered. The chime should sound if you left it connected.
6. reassemble the doorbell switch and apply double sided tape to the back of it and the back of the magnetic switch that is wired to it . Stick the switchs to the frame of the window that you want to protect. Use double sided tape and stick the magnetic portion of the magnetic switch to the window sash with the bottom of it level with the top of the wired portion of the magnetic switch. This will allow the switch to close and the alarm to trigger as the window is raised. It will only be closed momentarily as the magnetic portion slides past the wired portion of the magnetic switch. That is all you need to trigger the alarm and it uses almost no battery since the switch is only closed for the brief moment that the magnet slides past. This also allows you to open your windows without the contact draining the battery when the alarm system is off.
Step 4: Conclusion
You can make as many of the button switches that you want for all of the windows that you want to protect. For $7.00 usd apiece, I was able to buy just the buttons for the wireless doorbell that were on the same frequency. I used two magnetic switches on one button for the double windows in my house.
You might notice an extra wire coming out of the receiver. I added that as a longer antanae to try to increase the range a little bit.
If you have problems with the alarm triggering from a neighbors wireless doorbell you can follow the directions included with your doorbell on how to change the frequency.