Garage Car Parking Sensor Query

[_phillip]

Greetings,
I am looking for suggestions on how to trigger (wake up) a distance micro controller module when a garage door opens. This micro controller is not battery operated but powering down when not in use makes sense at the moment.

My 'basic concept' is this:
When an auto enters a garage I would like the driver to see a green LED on the wall in front of her. When the auto is sufficiently in the garage so that the garage door can safely close, the green LED will turn red, signifying that she can close the garage door.

I am proficient in crafting the distance sensor and the LED's. What I need is some guidance on how to 'wake up' the wall micro controller to begin monitoring the travel of the auto into the garage.

My garage door opener has a light that turns on when the door opens. This light could activate a light sensor wired to another micro controller (embedded in the garage door opener enclosure) which could use Bluetooth/BLE to trigger the wall micro controller, but using two micro controllers for this simple project seems like serious overkill to me. However, at the moment I see no other method to wake up the wall micro controller.

Thought: Does someone make a 'focused' light sensor module that could be aimed at the garage opener light? If so, that may work for this project and not require two micro controllers.

Any and all suggestions will be most welcome.

Thank you.

[adafruit_support_bill]

You could use a magnetic reed switch with a magnet mounted on the door, and the reed-switch mounted close by. When the door opens, the magnet will move with it and the switch will change state.

We have one in the store that is 'normally open'.
https://www.adafruit.com/product/375
But you can also find 'normally closed' types. If you use one of the normally closed types, you can simply route power to your microcontroller via the switch, so it will automatically shut off when the door closes.

[_phillip]

Thank you. I will take a look at those.