@Picbuster when my door is down it's down. Can't be opened because the garage door opener (GDO) doesn't allow for that. Post #1 the TS stated he has a Chamberlain. That's a GDO if I've ever heard of one. An automatic garage door position sensor such as I've built works nicely. AND it doe not require human intervention. Power failures? Rare. And usually don't happen for long. My GDO Closer circuit has several times a day it checks for an open door. If power goes out for one hour, the next sense period will close it. And my timer is battery backed up. In fact, I have one I just put away for the season. I used it for Christmas light timing. It keeps time well over a year without power. And if it goes dead in the meantime plugging it in charges the battery and you can reset the time. So if the one controlling my GDO should see a power failure, unless that failure is a year long - I'm going to discover it's open at some point.

 

Here is the circuit described in post #25. This can be expanded to any number of doors / windows / whatever.

Green indicates that all doors are closed. Red indicates that some combination of doors is open. You can combine D1 and D2 into a single, dual-color LED for a cleaner look. R1 should be a 1/4 W, axial type. For anything above 10 V, increase R1 to 1/2 W.

The green LED Vf (forward voltage) is less than the combination of the red LED and the signal diode. When all switches are closed, the green LED comes on and "shorts out" the red one. Adjust the value of R1 for your wall wart's peak output voltage and desired LED current.

NOTE: To use an AC-output wall wart (I have two left over from dead answering machines), add another diode across D2-D3, with the cathode toward R1.

ak

 

@AnalogKid Nice use of diodes. Wouldn't have thought of that myself.

 

Let's make it complicated. Position a magnetometer IC in the right place and detect open, closed and in between with one sensor. Assuming the door is vertical when closed and horizontal when open (along a ceiling). Mine follows pitched roof rafters but that's OK. Now, a steel door may be an issue for the magnetic field. I dunno. As the sensor goes "around the bend", you can watch the door move. Yes, yes, I know. Battery and wireless. Like I said, complicated.

 

Rosie the Robot from The Jetson's - send her out there every half hour to check if the door is open. Leave instructions when to close the door.

 

The nice thing about magnets and reed switches is that they have a narrow activation range. You get a signal only when the door is really closed, like within 1/2". That can be a problem for a people door, but is way good enough for a garage.

ak