How can I check remotely whether the garage door is open or closed?

May 7, 2004 9:44 AM

A method of determining the opened/closed status of my garage door [More inside]

My townhouse doesn't have indoor access to the garage, which means always having to walk outside to check if I remembered to close the garage door (very annoying when it's -30 outside). I'm trying to figure out a low cost method of determining whether the garage door is up or down.

I've thought of something along the lines of a LED in the hall closet next to the garage door opener which would turn on if the door is open. However I have little imagination in actually making it work.

Could anyone offer up a suggestion to rig such a device (and maybe provide a nice list of supplies I can take to Radio Shack to get it done?)

posted by smcniven to home & garden (6 comments total)

Low tech suggestion: is there a tree or something you could mount a small mirror on, that would let you see the door?

If not, there are wireless devices made to be attached to mailboxes to let you know when your mail arrives. I'd think it'd be fairly easy to persude one of those to do your bidding.
posted by duckstab at 9:59 AM on May 7, 2004

Limit switches. You could do one, and have a "Fully closed/ not fully clsoed" or "Fully open/not fully open" signal, or use two and have both. Wire them to some sort of light, or get fancy and bring the signal into a PC via the parallel port of with an IO card.
posted by skwm at 10:18 AM on May 7, 2004

Sears sells a monitor. A battery operated transmitter attaches to the door and a receiver plugs into an outlet in your house. They come with some of their door openers, but I think they also sell them separately at a pretty low price.
posted by caddis at 10:54 AM on May 7, 2004

go to tandy / radio shack and buy a reed switch that's normally closed, but opens when the magent comes near. stick the switch on the frame and the magent on the door. then all you need is an led, a battery and a bit of wire.

Assuming it's a small distance, it should be a piece of cake and you should be able to do it for under $10 (unless prices have rocketted).
posted by twine42 at 11:14 AM on May 7, 2004

If you can run wire from the door to a visible spot, then I think twine42's idea is the easiest route. So I'll expand on it a bit. (I apologize if I'm tellingyou stuff you already know.)

You can get reed switches by themselves (a small glass envelope with a wire coming out each end) or built into a little easily-mountable plastic block, intended as door-opening detectors for security systems. The plastic-block kind might even come with a matching magnet-in-a-plastic-block. You might need a stronger magnet though, since garage doors usually have more slop in them than house doors.

Then: an LED, a battery or a small wall-wart-style power supply, some wire, and (important) a current-limiting resistor to keep the LED from burning out. (Alternatively, use an incandescent bulb instead of the LED+resistor. Match the bulb's recommended voltage to the power supply's voltage.) If you leave out the resistor you'll get a nice bright LED but only for a while; it'll quickly overheat and go dim and eventually dark.

The resistor should probably be about 1kΩ (1000 ohms). If you want to calculate its value, take the power supply's voltage, subtract the LED's forward voltage drop (written on its package --- if not, guess at 2 volts), and divide that by the amount of current you want (again, the max. will be written on the package, or guess 10-20 milliamps). So for example, if you have a 12v battery, that's ( 12v - 2v ) / ( 10 mA ) = 1000 ohms.

Connect everything up in one big series circuit and there you go. If it doesn't work, try reversing the LED, since they only work in one direction.

FWIW, Radio Shack probably also sells flashing LEDs (they're LEDs with a tiny blinking circuit built in), which might be more visible, and might have a built-in current limiting resistor.
posted by hattifattener at 12:02 PM on May 7, 2004

Here's the zero hardware solution. Listen closely to the garage door. If you're lucky, it'll make slightly different noises when it's opening and closing. If it's too cold outside, just push the button and listen, and if you did the wrong thing, push the button again.
posted by tss at 6:21 PM on May 7, 2004