Door lock sensor for traditional key lock

So I’ve been looking for door lock sensors for a while now but nothing really suits my needs. I don’t want to use smart locks just yet as I feel like they are not secure enough right now.

I used a cheap Aqara door contact sensor and soldered a couple of wires with springs on the end to the reed switch inside, these springs sit in the strike plate and close the circuit when the deadbolt is inserted.

Luckily i have a pretty large cavity behind the strike plate so space wasnt an issue and the install was completly invisible too.

In home assistant I have changed the domain for the switch to be lock instead and it shows the correct state for “Locked” and “Unlocked”. For now I have my Google Nest Hub tell me the state of the lock, but I will be triggering notifications to the household if the house is empty and the door isnt locked.

Demo (with sound): VID_20210610_132235.mp4 - Google Drive

(Yes, i cut up an old bank card for my plastic inserts, I ended up taking the top insert out because there wasn’t enough space for the deadbolt to fully close.)


Cool idea. Well done.
Question, by any chance have a picture as to where you soldered those wires inside the aqara?

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I was supposed to but got carried away whilst working on it!

Inside there is a reed switch that looks like a green glass tube with two metal legs on either end. You solder a wire to each end to bypass the switch. You can then attach springs like I did or add a micro switch, proximity switch or even another reed switch.

I am doing another for my back door so will post a photo soon.

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Thanks! I will try, but would appreciate some photos on your second door lock sensor :slight_smile:

For me an ordinary push to close/open switch mounted behind the keep (with a hole that the plunger pokes through) has worked really well.

I tested with springs like OP but found it unreliable, was probably my install/ door etc

Moved to a Micro Switch today can tell a difference already will test for the next few days

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Proper job. For reliability I would turn the micro switch the other way up. That way any debris that accumulates will not get stuck in the micro switch. Great effort.

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How do you change the batteries in the in the aquara?

Reviving an old thread to add my solution to this as someone with a UPVC UK door with very little room in the keep side of the frame. Unlike many solutions that means I’m unable to fit a decent switch in there or extend the back to make more depth like on a wooden door.

I must have printed the 3d mount about 20 times before I got one that fit perfectly and didn’t obstruct the lock but this is my solution. Aqara contact sensor with the reed switch desoldered and re-placed on the mount. Magnet epoxy’d to end of bolt.

Goals for me are:

  • UK smart locks are still pretty poor and bulky, especially if you have a lift to lock multipoint system. I don’t need to lock the door, I just want to know it’s locked when out/going to bed.
  • Easy access to replace the battery in the device.
  • Longevity and reliability. Springs lose their “spring” and switches have finite lifespans (although we’d unlikely reach it).
  • No alterations to the door and the device must not be visible when the door is closed. You shouldn’t really know it’s there. So battery powered and no cables/boxes sticking out from the door frame.
  • No magnets drilled into the locking bolt. I don’t think my home insurance would think much of weakening the bolt.

Been running a few months now and very reliable. Time will tell but as there’s no parts to wear apart from the battery I’m not expecting any failures. Since I already have a 3D printer total cost was about a tenner. There’s a couple small tweaks to the mount that I’ll do before fitting the frontdoor one.


Neat! Would you share the 3D print file? You have my exact use case - uPVC door without much space. I’ve been trying to get a working sensor for this stubborn door for years!

Enjoy! Aqara contact door lock sensor by burg93 - Thingiverse

Thank you!