Hack a wireless doorbell into a wireless alarm switch or on/off switch

Picture of 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
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Step 1: Required Parts and components

Picture of Required Parts and components
2n2222 pinouts.jpg
(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

kgreene84 months ago
Hi. I need some help. Im using this to trigger a timer board for a model railway. The timer board needs a 12v supply, door bell need 5v so im using a voltage regulator. When i hook it all up the door bell burns out... So i tried adding a 3volt relay to the common and + of the transistor and it killed the door bell... Help!

While you can usually use voltage regulators as you've described, it sounds like your wiring may be askew, or possibly something got in and is shorting on the pcb. There isn't really much reason the bell should burn out. All you're doing in drawing power *from* it for the relay. In any case, you may want to have a look at optical isolators. Essentially an led, ldr, and (sometimes) transistor in an IC. They ensure complete electrical separation of the two circuits. You can buy them anywhere, or if you like, salvage them from lots of things (check out transformers, computer PSU's and the like)

fred413 years ago
I'm really interrested in your work, great job, I own a wireless door bell, but it doesn't produce a simple long sound, but 3 short bip, do you think it could work with your hack? If not do you know a solution to adapt it?

dagob4 years ago
Will the transitor keeps the alarm on untill you swithc it off?
deamonlord4 years ago
What can I do to simply on/off the lights in my room wirelessly? Obviously this wont work on high AC voltage but what will?
You can just use a relay switch with this method to control high volt ac voltage.
Just wire this to the relay's input and the high voltage as the output.
verdastel4 years ago
Cool project with affordable cost!
What do you think if you integrate IC 555 in the controller to control the frequency of the triggering signal (thus variable with some switches), and integrate IC LM2917 (frequency to voltage converter) to the receiver to turn it into a "several channel remote system"?
vinz.arthur4 years ago
should i still put a transistor even though it's not for the alarm?
jman 31 (author)  vinz.arthur4 years ago
Yes. The transistor is the key for turning the alternating current into a usable dc current. I will try to draw up a quick schematic for you when I get a minute to sit down.
vinz.arthur4 years ago
I need it for a project. Does the voltage will stabilize with the transistor?
jman 31 (author)  vinz.arthur4 years ago
I'm not sure what you are asking. The 220 voltage will be stable if that is what you mean. The voltage that you apply to open and close the relay will need to be a stable DC 5 volts. You can either use a battery for this or get/make a 5v circuit that works off of the 220. That is what I would do. There are plenty of DC wall jacks (wallwarts) that you could use for this.
vinz.arthur4 years ago
Is there other way to make it a switch for a 220v socket?
jman 31 (author)  vinz.arthur4 years ago
Probably cheaper and easier to get one of these:
jman 31 (author)  vinz.arthur4 years ago
Sure. As long as your relay is rated for 220 you can put whatever you want on the switch side of the relay. You will want to put a fly-back diode on the low voltage side of the relay. You can Google it, but a quick search brought up this page: Be careful if you are new to this working with mains level voltage. You might want to get someone that is familiar with it to help you if you aren't
vinz.arthur4 years ago
Hi I would like to know what is the output voltage to the speaker? I want to convert it to a relay switch instead of the speaker. By the way I'm a newbie another question is what is the purpose of the transistor. thanks( I wish I would have the reply as soon as possible)
jman 31 (author)  vinz.arthur4 years ago
The output voltage is variable with the sound so there is no way to just use a relay switch. You can however add a battery and feed power through the transistor so that it completes the circuit and closes the relay. Pretty simple to do. The transistor is there simply to turn the variable pulse from the speaker outputs into a basic on/off switch. When there is no sound, the transistor is open. As soon as there is sound it causes the transistor to close, completing the circuit for the alarm.
Thank you very much for that information!
Follow up question, Is there any other way to make a switch for a 220v socket? I'm sorry for annoying you.
Lydboots4 years ago
Hi - I don't quite understand your title (regarding the "switch")
can you tell me if this would do the following job please:
I want an alarm to go off at some distance away (wirelessly) when a door opens
not a door bell but an entry alarm
jman 31 (author)  Lydboots4 years ago
All this instructable does is replace the magnetic switch that would normally trigger an alarm with a wireless one. You still either have to build or buy the alarm system. Sorry it took me so long to answer this, I missed it somehow. Let me know if you are still confused by this.
fungodude4 years ago
I have a wireless doorbell with 2 speakers. Does this matter??? Do i just hook up the transistor to one of the speakers or what???
jman 31 (author)  fungodude4 years ago
Yes. The doorbell puts out alternating current in the form of sound waves. You use this current to "turn on" the transistor. I would check and make sure the sound is indeed coming out of the speaker that you decide to use. Let me know if you have any other questions.
fungodude4 years ago
I have a wireless doorbell with 2 speakers. Does this matter??? Do i just hook up the transistor to one of the speakers or what??? Please Help.
matchett5 years ago
what is the point of having th transistor, and if im just hooking two wires to the ones that go to the speaker do i still need it to turn it on/off? thanks
jman 31 (author)  matchett5 years ago
The transistor turns current from the bell into a momentary switch that the alarm can use. The alarm doesn't trigger from current, it triggers from the completion of the alarm circuit which the transistor provides.

Not sure what you are referring to on the second question. Could you elaborate a little? Turn what on/off?
i am making an airsoft gun that fires remotely. i have two wires that when they touch it shoots, so i was going to hook the up to the wies that run to the speakers. so when the bell is suppose to ring it will hopefully shoot.
jman 31 (author)  matchett5 years ago
Yep, you need the transistor. That is the same situation. You have turned the wires into a momentary switch. Any small signal npn transistor should work for that. Just look at the datasheet so that you get the pins right. You don't want to just connect the wires to it because it will be shorting the bell directly to ground. If you get a transistor and you need help with the pinout, just let me know.
jman 31 (author) 5 years ago
Thanks guys.

Wolf, when time permits I will see about editing step 3.

Stephenniall, I hope you will post you work so we can enjoy it. I built my alarm system from this pdf. . It seems to work really good so far. You have to have a basic knowledge of putting a hex file on an IC though and some electronics experience. You can get all of the files for this alarm system here on my little DIY forum.
You may have to register to view the files. All of the files (including programming) are included in the zip file.
Smart Idea !

Im currently designing a Cheap multi room alarm Thats cheap (under 10£ about 25$ ) to make
Wolf Seril5 years ago
Very cool idea, well done. Consider splitting step three into a few more steps, though.