My objective was to have a visual indicator on the interior wall that showed that the garage door was open during the day and once it got dark outside an audible one to indicate that it had been left open. I used a simple circuit using two common IC's that only receive power once the garage door is opened. During the day the switch plate shows a single red blinking led to indicate the garage is open. Once it gets dark outside the blinking red led is accompanied by a white led and an audible buzzer that beeps, letting you know the garage is open. The circuit uses a cds sensor to detect the amount of light outside in conjunction with a potentiometer that can be used to adjust the light sensitivity.
Step 1: Video Showing How It Works
Above I have embeded a Video Showing How it works this is the link http://www.youtube.com/watch?v=mZqPcMN7284
Step 2: Prototyping the Circuit
Only a handful of parts are required for this circuit and for the build even less, a pcb, case, various wires and a piece of metal to mount the switch. I used the following components (Microswitch, power adapter 5volt 75ma, cds sensor, red led, white led, buzzer, lm555, lm3909, 2 470uf capacitors, 1K and 10k resistors, and a 20k potentiometer). The capacitors don't have to be exact they control the speed at which the led's / buzzer turn on and off at. Also you could use a larger potentiometer but by doing so you would lose fine incremental control over when the lm555 will begin oscillating.
Step 3: The Build
I used an existing bolt on the garage door rail to attach the switch using a piece of metal bent into an L shape. To ensure good contact I added a piece of plastic to the switch to widen its contact surface. After that I waterproofed the cds sensor and sent it through a vent hole in the garage that comes out under the eave. As far as the indicators on the switch plate I used hot glue to keep the led's in place and drilled some holes in the center for the buzzer. I then drilled through the wall into the garage to route the wires to the circuit. I soldered the circuit together on a small blank circuit board and used a small pill box from the dollar store as an enclosure.