Car key in the house - Looking for a weight sensor or any ideas? :)


I want to implement the following idea: My car key has a fixed place in a bowl. My idea is: Open the garage when the key is taken and close it when the key is in the bowl.

For that, I want to create a small box as replacement for the bowl. In this box, there is a weight sensor. If the key is in the box, the weight is higher than without the key.

Now I am looking for a zigbee weight sensor. Do you know any that works with hubitat?

Alternatively, I am thinking about something like a physical scale with a spring. And then use a contact sensor. When the key is in the box, the scale is pushed down and the contact sensor notifies: open.

Or do you have another idea for checking if the car key is in the house or not?



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What a cool idea.

You could probably do the same thing with the box on a small seesaw. It's up/open without the weight of the keys and down/closed with the weight of the keys. My only concern is how far it would have to move to register the open/close.

You could use a door open/close sensor and put a small magnet on your keychain. It might require some relatively precise placement of the keys, though.

You might be able to use a sensor with exterior probes (like a water sensor?) and somehow open and close the circuit as well.


I'm not sure what the key weight is but you could use one of these:

plugged into a Ecolink Door sensor.

I used one for a pool shower. I had a bamboo mat and the Force Sensitive resister was "pinched" when someone stood on the mat.

The thing is pretty sensitive and just pinching it between my fingers was enough to trigger the Door Sensor.

It's direct wire for me... the two ends of the force resister plug perfectly into the screw contacts on the inside of the door sensor.

I'd start with a box deep enough for the keys and a slab of wood. the Force Resister is under the slab with a hard bumper that focuses the weight onto the Force Resister.

Screen Shot 2022-11-23 at 12.32.31 PM


Uhhh, that is awesome. Thank you!

Key weight... I meant the weight of the key :smiley:

I will check this!


According the Magic 8 Ball (Google) Avg key weight is ~0.28oz, keyfobs ~3.8oz

Ah sorry, thought it was a spelling mistake on my side :smiley:

My key is not the lightest one... I will try this sensor!


Wow that is a great idea for sure, when I read the OP I was thinking a cherry micro-switch for easy implementation with an Ecolink Door Switch.

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Uhhh also very nice thank you :slight_smile:


You could just put a Z Wave or Zigbee contact in your box and attach a slim self adhesive magnetic coin to the key - that'd work fine.


I would second the contact sensor recommendation. Unless there's some reason you can't have a magnet on your keychain, I suspect this would be easier to set up.

What do you think: I often have my key next to my smartphone and wallet with credit card. Could this be an issue when I have a magnet on my key?

You might clip a small magnet on your car keys and have a contact sensor in the bowl/box.

This seems potentially risky if there is a false-positive trigger event that opens the garage door inadvertently. Take care to build in logic that restricts the automation from occurring in the middle of the night, when you’re not home, etc.

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You've gotten some cool replies. I especially like the FSR. Been looking for something like that for other uses.

BUT....I urge you to consider when you may need, or be forced, to pick up those keys/keyfob and ABSOLUTELY DO NOT want that garage door opening. (And woe if you have kids/grandkids!)

I can think of a few situations that are harmless and might just have someone walking out to an open door in their PJs ...but consider when that door is a part of your security barrier and when a preemptive opening might increase your risk factor.


I have to agree that opening the garage door with an automation is kind of scary and I would not do it, but closing the door after you arrived, seems safe enough as long as the door has all it's safety measures in place like the beam at the bottom of the tracks and others like auto reverse if something is in the way.

You might also want to have some kind of a timer that when the garage door is closing, check after some 20-30 seconds if the door is actually closed or not in case something prevented it from closing.

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