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