Infrared Intruder Alert




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Stop intruders from trespassing on your property with this infrared alarm system.

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Step 1: What You Need

1. Garage Door Sensors like these
2. Wireless Doorbell Chime for $6
3. Photocell
4. Various components as shown in the schematic.
5. 5 Volt AC Adapter. You need a regulated supply so the voltage does not 'float'. A 1.0 Amp supply will typically be regulated.

Step 2: Prepare the Receiving Sensor

I tried to get inside the garage door sensor to access the circuit but after a bit of prying decided that it would be better to leave it intact and keep the waterproof design as it was clear the case was glued together. So, using a photocell over the receiver LED was the best option.

1. Epoxy the photocell to the receiver to prevent any light from getting to the cell. I also added some coats of spray paint as these cells are extremely sensitive to light.

NOTE: To see which is the receiver, you can power up the sensors by using 3-4 "AA" batteries (4.5-6 volts). Connecting a 100ohm resistor connected to one of the sensor positive (+) lines will tell you which is the receiver when they both light up.

Step 3: Build the Circuit

The circuit is designed so the photocell triggers the 6 volt relay which in turn closes the switch on the transmitter, sending the signal to the receiver and ringing the chime. I built it as small as possible because I wanted everything to fit inside the smallest Radio Shack hobby box.

Step 4: Finish It

Install the new circuit along with the transmitter circuit inside the hobby box. I drilled 3 small holes. Two on the side for the wiring that goes to the sensor transmitter/receiver and power and one more hole on the bottom that the leads for the photocell would fit inside. I also used rubber grommets and silicone to seal those holes. I used "5-Minute" epoxy to glue the box to the bracket that came with the garage door sensors.

Step 5: Use It

Install the sensor transmitter and the receiver wherever you want to use it. They come with around 30 feet of wire. Power it up and when the beam is crossed, the doorbell transmitter should signal the receiver and you will hear a chime whenever the beam is broken.

I hope you enjoyed this Instructable!



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    84 Discussions


    Question 1 year ago on Introduction

    Can you say exactly the brand/model of garage door sensors you used? Mine are such that the LED pulses off instead of on - and seems that would not work with the photocell.
    Merely supplying a link to Ebay not so useful after 8 years.

    Also, any reason not to use 12v adapter instead of 5v in order to use a louder alarm?
    I also intend to insert a timer into the circuit so it will stay on or be intermittent for a certain period. Suggestions on that?



    6 years ago

    Replace the chime with several Li- Po batteries with a timed switch and a capacitor, put it at the entrance to your house, and when they arrive... Flaming doorway, what burgalar wouldn't think twice?


    6 years ago on Step 2

    "Epoxy the photocell to the receiver to prevent any light from getting to the cell"
    This statement is confusing to me and a few others, surely this will block the receiver?, but after reading the preceding sentence
    "So, using a photocell over the receiver LED was the best option"
    I am no longer confused, If I may make a suggestion you could reword the statement.

    "Epoxy the photocell to the receiver LED, to detect the LED turning, on and prevent any light from getting to the photocell"

    Is it possible to hook this up to a phone? So it calls you about an intruder while you are away?


    8 years ago on Step 3

    does anyone know of a substitute for the transistor i cant find them at radio shack or online?

    1 reply

    Reply 6 years ago on Step 3

    In a circuit such as this the transistor is not super critical. Use a PN2222 or even a 2N2222 and it will be fine.


    7 years ago on Step 3

    I have several questions:
    1 Is the 100ohm used as a limiting resitor for Receiver??
    2 Why is it not used for the Transmitter?
    - Is the Transmitter and Receiver part of the garage door system??
    If it is then glueing the photocell over the Receiver will cause the garage door not able to work.
    3 What energizes the photocel - How? What light source is used? since the photocel is glues over the Receivers 'light input' so not allowing to get any light from the Receiver!
    I drew your diagram out on a schematic to be able to folow the circuit closely and as I can see it when the phtocell is energized [ I donot know how?] This will turn on the transister and in turn will turn on the relay!!!!!
    I dont see the connection of the circuit in rlation to the Transmittter and Receiver!
    I believe if you drew a schematic of the entire circuit I'm sure that your project would be much clearer to understand!
    At lest for me - thanks


    10 years ago on Introduction

    now you know when the crazy man down the street has gone crazy and is planning to kill you with an axe!

    6 replies

    Reply 9 years ago on Introduction

    oh no! you better duct tape it back on! lol

    maybe you could surround your house by building a few of these


    8 years ago on Introduction

    Replace the chime with a relay detonating a firecracker. :D


    9 years ago on Introduction

    when the beam i crossed does the alarm continue to go off or just when the beam is crossed for that 1 sec.?