Introduction: How to Install a "garage Door Open" Indicator

Picture of How to Install a "garage Door Open" Indicator

Ever left your garage door open overnight? In addition to being a terrible energy waster, all the tools, bikes, and other stuff are available to thieves - who might even enter your home via the door from your garage to your living quarters.

Install a simple indicator which will alert you if you've left the garage door open. Total cost is less than $30-$40, and you can determine exactly where the indicator will be located.

What you'll need:

-A 24 volt doorbell transformer
-1 push button "normally open/momentarily closed" switch
-1 red LED - 2.8 volts
-1 4.7k-Ohm resistor (specific part numbers for the electrical components are provided in Step 2)
-2 strand bell wire
-Electrical tape and/or heat shrink tubing

-Wire strippers
-Soldering iron + solder
-Electric drill
-Misc. hand tools - wrenches, etc. - depending upon the specifics of your installation

Let's get started...

Step 1: Identify a Switch Location

Picture of Identify a Switch Location

Your first step will be to determine where you can put a switch to close the indicator LED circuit.

When I looked at my garage door, I noticed that a piece of galvanized trim on the top of the door stopped right next to the angle iron used to hang the door tracks when the door was in the fully opened position.

I bought a simple corner or "L" bracket and mounted it from the bolt that connected the wheel track of the door to the vertical angle iron bracket. A simple Radio Shack "normally open/momentary close" push button then mounted on the other side of the corner bracket, with the switch of course facing the top of the door.

By bending the bracket slightly, I was able to ensure that the switch was fully depressed every time the door was fully opened.

This arrangement might work for you, or you might have to improvise a bit. You of course want to mount the switch in a manner that it's in the "closed" position when the door is open.

NOTE: in the image below, I stopped the door's movement before it reached the fully open position so you could see the orientation of the switch in relation to the top of the door. When the door is fully open, the red push button is fully depressed, and the circuit is closed. (See 2nd picture below.)

Step 2: Wiring Diagram

Picture of Wiring Diagram

Before we go any further, a simple wiring diagram.

The system uses a 24 volt doorbell transformer as the power source; a 4.7k-Ohm resistor knocks the voltage down to that required by the LED (~2.8 volts.)

All of the electrical components are available at Radio Shack and will cost approximately $6.

In addition, you'll need some 2 strand bell wire; how much depends upon where you plan to put the LED. More on this later.

All of the Rat Shack part numbers are indicated in the diagram.

Let's take a look at how I mounted the doorbell transformer in the next step...

Step 3: Wiring the Transformer

Picture of Wiring the Transformer

I used a variable voltage (8-16-24 volt) doorbell transformer made by Heath/Zenith. It cost about $15 at my local home center. You need a transformer that produces 24 volts.

I direct wired the transformer to a grounded, 3 prong plug and mounted it directly above a power strip near my workbench. The 4.7k-Ohm resistor was soldered in place and then secured with a piece of heat shrink tubing I had on hand; it's directly beneath the transformer in this picture.

If you wish, you could cover the wiring with plastic channel for a neater appearance; I simply chose to use insulated staples.

One other thing I did later on was to plug the power strip into a lamp timer, and set the timer so the strip is on only between 8pm and midnight. There's no reason to power the transformer 24/7, as the only critical time is at night when we're going to bed and (presumably) have forgotten to close the garage door. Which leads us to the final step...

Step 4: Install the Red LED Indicator

Picture of Install the Red LED Indicator

After thinking about this for a bit, I figured that the absolute best location for the "door open" indicator was in the master bedroom.

It could have gone in the kitchen, or mud room (whose door connects to the garage) but my logic was "if I could remember to look at an indicator in one of those rooms, I could just as easily remember to open the mud room door and check the garage door."

To be absolutely foolproof, I thought it had to be in the master bedroom. Looking around the room, I thought of getting at the ceiling light fixture via the attic, and perhaps placing the LED inside the light's frosted globe.

In the end, I decided to drill a small hole in the decorative trim on the light, oriented so it faces the head of our bed. That way, if the LED was illuminated, you couldn't help but notice it when you went to bed.

I was able to route the wire from the garage all the way through the attic to the location of the master's ceiling light. (NOTE: this was the most time consuming step in this project.) Working from the bedroom, I drilled a small hole next to the light's electrical box, within the diameter of the light itself. I then fished the wire through from the attic, and made the connections to the LED. (As with the resistor, the wires were soldered to the LED's leads, and everything secured with heat shrink tubing. You could use electrical tape for this; just make certain everything is sealed really well.)

And that's it. As mentioned earlier, I put the system on a lamp timer so it's operational only in the evening.

It works perfectly, and we're now assured that if we forget to close the garage door before retiring, the LED will bring us back to our senses.

Total cost of this project was around $40, and that included 120 feet of bell wire. YMMV; bell wire costs about $ .20 per foot.

If you've read this far and enjoyed this project, please consider visiting my blog - Practical Hacks - at


roybrew (author)2016-11-22

Is the white bell wire connected to the transformer? So, it seems like I
need to run the bell wires from the push button switch, with the white
going directly to the LED and red heading INTO the transformer and then
another red segment heading OUT OF the transformer, with the resistor
soldered in-line, and going to the other connector on the LED. Is this
correct? Additionally, if I were to modify this design for a 2-door application, I would need a separate resistor for the 2nd door correct? Or not?

RaymondC2 (author)2015-11-26

The mission objective and notification LED is brilliant! As I understand it the way the switch is mounted: it senses that door is either fully-open or not fully-open. I would be interested in photos of sensors that confirm that the door is fully-closed or not fully-closed. The distinction is that in the photographed configuration, there is the possibility that the door is partially open, which would not trip the switch (LED notification). Again, this would be perfect reminder for renters that leave the door open.

scannon5 (author)2013-10-04

I need something like this (or this exactly, in fact) because I have backed into my garage door too often, in too big a hurry to back out. This last time I backed out so quickly that we had to replace the door. I am going to install this to fully indicate that the door has opened, so it is clear for me to back out (No comments about women drivers, please!).

I have a commercial position indicator, but that won't quite work. The sensor detects whether it is vertical (door supposedly closed) or horizontal (mostly open). It does not indicate whether it is 100% fully open or closed.

So I will install this and put the LED (green for my installation) in my line of sight right there in the garage. Maybe I'll even get creative and make a sign that lights up that says "OK" or something.

ydoucare (author)scannon52015-06-02

Never backed into my garage door like this. Just wait for the door to open, then back out, not hard to do. Really, wth? Backing into your garage door is a normal occurrence? lol

scannon5 (author)ydoucare2015-06-02

I have three dogs that get rather chaotic when it's time to go for a "R-I-D-E." And one dog needs help getting in the car. Usually I open the door when we go into the garage, but if they are super chaotic for some reason, it has happened a couple of times that I think I opened it, but didn't. Our biggest is a Great Pyrenees, and if he gets in the way of the rear view mirror, I can't see a thing out the back.

Sh*t happens, what can I say?

fbIsAStupidPeiceOfCrap (author)2015-04-16

I would think a better way to do this is to use a normally closed switch and mount it so it is pressed when the door is in a fully closed position. That way if the garage door is partially open the switch would be pressed.

Gary567 (author)2015-01-27

Thanks Journeymanjoe for pointing out code violations. You are right the average DIY homeowner might not know these things. (Unless that person is also a Electrician) None of us would like a house fire...that would be way more costly then hiring a qualified repair person. I did find a helpful site if you all want to fix some other things...some of our rollers got unscrewed and fell the whole attachment came off.

journeymanjoe (author)2014-04-17

Step #3 is a National Electrical Code violation and a hazard to anyone that comes near it! You can't have exposed energized parts over 50V (should be installed mounted to a box with the 120V wires inside the box), that is why they make these transformers (primary side is 120V and the secondary is 24V). It is a violation to use single conductors with this plug (the plug is made for use with a cable).

Step #4 is a National Electrical Code violation also, you can't modify a listed luminaire (drilling the hole in it); you can't mix the low voltage with the 120V power in the luminaire.

This is why homeowners shouldn't be doing electrical work, too often we hear about residential fires blamed on bad electrical wiring (would be nice to know how many were wired by the homeowner)! Please hire a professional, licensed electrician to do any wiring. The money you save by doing it yourself is not worth the risk to your life and property.

Cambenora (author)2013-02-24

I have built a very similar setup for the same reason. I've used the doorbell itself as a "base station"; the LED is mounted inside the doorbell housing which is located in the main living area in a prominent position. The doorbell runs on four "D" cells, and I siphon off 3V from two of the batteries to power the indicator.
I notice you say "You need a transformer that produces 24 volts." Is this to overcome the resistance in the wire over the long distance to the garage door? I found the 3V from the batteries works fine on mine, and the wire goes for about 20m (60ft). I think there is a loss over that distance but the LED draws so little current that it doesn't matter.
Great instructable, kjc2010. We're obviously thinking along the same lines!

mcory (author)2012-10-18

You state that there is no reason to power the transformer 24/7 and I agree.

Couldn't you wire this thing to power the transformer only when the door is open? The simplest way might require passing 120v thru your switch.

normanschneider (author)2011-10-06
Great project and well documented. I had a similar thoughts around this very same project idea. However I do have some concerns that may have already been stated or otherwise addressed within the threads of this conversation:
  • This project appears to address a garage door being in the "fully open" position rather than indicating that the door is "closed" (completely shut and secure).
  • The use of a push-button switch would lend itself over a period of time to be pushed out of range should the door or the switch be moved or otherwise become misaligned.
  • Use of a "leather finger" (mentioned earlier in the thread) might address the above alignment issue, however it might be subject to temperature or other physical factors requiring additional maintenance.
  • This solution might not address multiple garage doors that are more common place in today's homes. Likely this requires a slight modification to the project to address this situation.
  • This solution requires running wire back to the interior of the house (e.g. master bedroom)
Having just begun tinkering with Arduino platform, I might suggest an alternative approach that might address these issues:
  • Single Arduino microprocessor plugged into garage wall-outlet and mounted near garage doors
  • Each garage door to be outfitted with window security-type magnets near top of interior door frame
  • Install sensor (Hall-Effect or Reed) aligned to magnets when door is in a fully-closed position
  • Each sensor is hard-wired to (separate pins of) the Arduino microprocessor
  • Appropriate Arduino code/logic is uploaded to monitor state of each sensor
Once the Arduino remote monitoring device is installed, additional Arduino communication "shields" (extensions) could be installed to advise the homeowner on the current/changed state of each individual garage doors.

My current thoughts include the following scenarios to exploit the logic programming and features of Arduino:
  • Wireless Ethernet to send email or SMS when a door is opened/closed during unscheduled period (e.g. work hours)
  • Update a website status when door is opened/closed (e.g. Ethernet wirshield)
  • Allow your cell to communicate back to Arduino for further action (e.g. close door)
  • Sound chime in house when doors are open longer than X minutes (use Arduino logic)
  • Sound alarm in house when doors are opened anytime from 12AM to 7AM (use Arduino logic)
  • Implement X-10 interface to light up a lamp or chime an alarm (alternative to tie into X10 automation)
  • Install RFID sensor on exterior of garage wall to allow for kids to use RFID style key-fob to enter house via garage.
  • Maintain a log of all openings/closings over period of time (e.g. write to internal or external log file)
While not all of the above scenarios will be adopted by the reader, it just shows that you are only limited by your imaginations. I hope to begin work on this project and will promise to share/post my results in this forum.

jmosk (author)normanschneider2012-02-16

Great minds think alike as they say.I juat came across this post as I was curious if anyone else implemented what I put together. I built exactly what this person had suggested. I have a WiFi Arduino board connected to my 3 garage doors. I installed a door alarm magnetic reed switch on each door to determine its open/closed state. If any door is open for more than 5 minutes, a Tweet is sent to my wife's cell phone and an Email is sent to my Blackberry to tell us the state of all 3 garage doors. Only when all 3 doors are closed again do we get another message to tell us everything is back to normal.

My wife is always concerned that she may have left the garage door open when she leaves and now she only needs to look at her mobile phone.

schroedc (author)jmosk2012-09-19

instructable? I'm very interested in doing this, so please create one!

frankpadams (author)2012-02-24

Most garage doors already have a light on them indicating that it's open. Wouldn't it be much simpler to connect a socket receptacle to the existing light and just run the power to any light in the house? You may be over-thinking this one.

Handy_Andy (author)2011-02-27

It's been said already, but you could run 4 conductor wire (telephone or CAT3) and have the other 2 wires hooked up to the switch for the opener. Then you could close it from within your bedroom. I'd probably recommend a reed switch (switch activated by a magnet) inside that same light fixture, and then you could just wave a magnet by it. Wait 20 seconds, and when the light goes out, the door is closed. Either way, very nice project. Definitely going on my to do list.

3366carlos (author)2010-09-26

Nice idea, i believe with the proper calculations/components you can use 120vac, no need for a transformer. LEDs only drop 0.7v, so find the appropriate resistor value to limit the current. CAUTION: when working with 120VAC a certified electrician is required.

Handy_Andy (author)3366carlos2011-02-27

Sort of. AC is tricky because it's a sine wave, and therefore is only positive half the time. Also, the resistor would get SUPER hot. Here's a really good Instructable (not mine) about using LEDs with AC power:
I agree, bypassing a transformer (especially a $15 one) would be the most efficient.

baudeagle (author)2009-11-22

Great Idea, I am thinking about doing something similar to this but I am considering using a magnetic reed switch instead of a momentary button.

kill-a-watt (author)2009-09-20

neato! I'd check the draw of the timer itself vs. just leaving the transformer on all the time. While it's a nice idea, if there's a small motor in the timer it may take much more juice than the very small load the transformer takes in the off phantom load. If I could only think of a tool to measure the power... seriously, I've plugged 8 wall warts into a power strip and run them for weeks with a kill-a-watt power meter. I've found, despite all the gloom about phantom loads, that the wall warts really don't take all that much juice when they are not being used. You could counteract a year's worth of this transformer idling (light off, garage door down) easy by just deciding to line-dry one load of laundry per year. I'd also like to note that you could probably get away with using an old 9v. cell phone charger wall-wart or something if you recalculated the resister and the resistance of your run of wire.

kjc2010 (author)kill-a-watt2009-09-20

Great comments... thanks. I'll consider switching to a wall wart!

kill-a-watt (author)kjc20102009-09-20

what I meant was this. I have a bunch of old wall-wart type phone chargers in the junk box. If I were to build this (and I probably will, I just hate the idea of pulling the wire up three floors into the attic), I'd use one of those rather than buy something that put out 24 volts. <- should help with other voltages.

wperry1 (author)kill-a-watt2009-09-28

One more thing to consider is that most wall warts put out DC voltage which doesn't travel well over long distances, especially at low voltages on small gauge wire. The straight transformer puts out AC which is much better suited to running long distances.

kill-a-watt (author)wperry12009-10-17

True, but you could calculate the resistance (or measure it with a DMM) and then put that into your equation for lighting the LED just like it was a normal resister.

Of course, the property that lets AC travel long distances with minimal loss is the high voltage, not the type of current. AC is easy to step up and down using  transformers, which is why it is used. Edison's DC system needed a power plant every mile.

Since you only need say 30 millawatts for one led, I don't think the voltage drop is really that bad. Maybe a few ohms at most depending on gauge.

rbrown3rd (author)kill-a-watt2009-09-27

What I would find more useful is a way to have an indicator in the car. It would work like this. You back out of the drive way in a hurry to get to work. You forget to close the garage door. A sensor in the car detects the position of the door. If it is up and you start out of the driveway it would light an LED or sound and alarm. Triggered by proximity distance from door? If you drive away and it is down nothing would happen. Is that possible?

kill-a-watt (author)kill-a-watt2009-10-17

following up, I've plugged one timer into a kill-a-watt and left it for two days, no power was measured. I suppose it's less power-hungry than I thought.

Kasm279 (author)kill-a-watt2009-10-08

lol wall wart

gumbytig (author)2009-10-01

Great ible. I've been thinking of doing something similar for leaving the lights on in the garage all night like I keep doing. I could just wire the transformer in to one of the switched wires to the lights and get the same effect. I wasn't thinking of a bell transformer. that's a great idea. Thanks.

Kasm279 (author)gumbytig2009-10-08

a photoresistor in the light might be easier (in the plasic housing, pointed at the bulb)

gumbytig (author)Kasm2792009-10-09

yeh but i've already got the bell transformer in the crawl space from the previous owner who had a hard wired bell and then switched to a wireless which now doesn't work.  I wish i could find the old wire but i'm not gonna go hunting the old bell hole through vinyl siding. 

HARSHAD BHATT (author)2009-10-01


Kasm279 (author)HARSHAD BHATT2009-10-08

woah caps ill be bold :P

haruspex (author)HARSHAD BHATT2009-10-01

If everything is emphasized, then nothing is emphasized. Please turn off your Caps Lock, it only serves to aggravate people and make things difficult to read. Thank you.

HARSHAD BHATT (author)haruspex2009-10-02

I am sorry, I will definitely be more careful.

Waggie22 (author)2009-10-01

Problem is - when the door is not all the way open, you don't know - but it is not closed. Adapt your bracket, move it to the other end position i.e. door closed and use a normally closed switch. This would cause the door to only extinguish the LED once it is firmly shut. Voila!

Kasm279 (author)Waggie222009-10-08

or you could have the switch short the circut, does the same thing

bud-d (author)Waggie222009-10-07

Thanks, this makes more sense for me cause I have a detached garage.  Also it is a case of shutting the barn door after the horse is out.  Lost two chain saws after leaving it open all night.  Will get to radio shack today and get this project started and finished asap 


Jackie_A (author)Waggie222009-10-04

You are right, relocating the sensor switch to detect when the door is closed would be better... And if you keep using a normally open switch but make it feed your transformer primary... now when the door is "not closed all the way" the switch closes and the LED is powered on. Voila! no need for the lamp timer either!!

kjc2010 (author)Jackie_A2009-10-04

I think I mentioned earlier, but just in case: we occasionally leave the door open 4-6" for ventilation. In that case, I don't want the LED to be illuminated. My only interest is when I've totally forgotten that I've left the door wide open in the evening.

dalesd (author)2009-10-04

I have one of those Smarthome wireless garage door indicator systems, and it's not very good. I may do this instructible. I have a detached garage, so I'll have to dig to run the wires. I'll also modify the circuit a little. Use a DPDT switch and you can light a red LED when the door is open, and a green LED when the door is closed. Even better, use one of those bi-color red/green LEDs with a polarity reversing DPDT switch circuit. I'd also use a 12v wall-wart transformer, and a reed or micro switch.

Orange Guy (author)2009-10-01

I really want something like this on my garage because there are a lot of goodies in there and I have been known to leave the door open. Alas, it is not at attached garage and there's no easy way to get the wire from the garage to the house. Any thoughts on how to handle that?

srilyk (author)Orange Guy2009-10-02

If you have a window near your house you could use a laser pointer and some type of prism to make it a little more evident. Of course I'm not sure what kind of life expectancy one would get from a laser diode, but then again you can pick some cheapo ones up at the dollar store, so it's not a terribly expensive test. If the life was good you could also use a photodiode (or possibly an LED) mounted near the window. Of course, Blue Flamer has already posted some much easier ideas.

Blue Flamer (author)Orange Guy2009-10-01

Orange Guy. Not hard to do if you have power already in the garage. You just have to run the bell wire to the house. Two ways to do that: 1) Go underground. Dig a trench and run the bell wire through a conduit pipe to protect it.. This could be pricey, time consuming and hard on the back depending on the distance. 2) Go overhead. Get some of the plastic coated clothes line and a couple of reasonably "heavy duty" eye bolts from Home Depot, Lowe's or your local hardware store. Secure the clothes line between the eye bolts and wrap the bell wire around the line. Even if you do not have power to the garage, all you need is to connect the wire to the switch on the garage door. Either way, you are only running 12 to 24 volts of power either way it is done. Two words of caution on the overhead route. 1) Use at least 18 Gauge thermostat wire that has the secondary outer wrapping around the wires. 2) When your foot hits the first step of the ladder use extreme caution and observe ALL safety practices and common sense while on the ladder and when placing it in position. Good luck. Blue Flamer.

heathbar64 (author)Orange Guy2009-10-01

I once purchjased from the discount bin, a wireless thing to do this, it had a tilt switch that you attached to the door, and a reciever you mounted to the wall in the house. I don't even remember where i got it.

Sunbringer (author)2009-10-01

The wireless solutions require a battery in the transmitter, and then they fail, it is a pain to get a new one to replace it. I'll probably ditch mine in favor of this solution. I appreciate the simplicity of it.

srilyk (author)Sunbringer2009-10-02

You could pick up the proper voltage transformer at a thrift store for < $5 most likely (usually phone chargers) and just use the DC from the transformer in place of batteries.

rimar2000 (author)2009-09-20

Sometimes I thought to do something as this, because although the possibility is small, the risk is ENORMOUS. You've convinced me, I will note it in the list of pending tasks.

fin saunders (author)rimar20002009-10-01

I'd recommend a second switch that indicated that the door is fully closed. It's just another switch and LED. Vacations? I unplug the garage door opener. Nearly as good as a lock and can't be hacked. Well hacksawed, but not transmitter-style hacked. Cheers, Fin

propertydoctor (author)2009-09-27

I love the concept of this 'able but, one flaw is evident to me. The position of the switch does NOT indicate that the door is closed. To insure that the door is in fact closed, the switch should be a "normally closed" device and placed so that it is compressed (thereby turning off the indicator LED) when the door is fully closed.

wa7jos (author)propertydoctor2009-10-01

You might also consider a magnetic door/window "security system" switch. It has screw terminals for the wires and is easy to mount and not too fussy to adjust. I built something similar to this years ago, and that's what I used. Works great.

kjc2010 (author)propertydoctor2009-09-27

PropertyDoc: In the main photo in Step 2, I'd stopped the movement of the door before it was fully open, so you could see the orientation of the switch and the top of the door. When the door is open all the way, the push button is depressed, closing the circuit. I've added a 2nd photo to that step to better illustrate how it works. Sorry for any confusion!

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