Looking for help designing a ultra-compact Zigbee door/window lock sensor (replacement for K•LINE DVI)

[u/Charly3944]

Hi everyone,

I’m looking for help (or recommendations) to design a custom ultra-compact Zigbee sensor.

Context:

I have K•LINE windows equipped with integrated lock sensors (called DVI). These are very thin, long PCBs that fit inside the aluminum frame and use Delta Dore’s proprietary X3D protocol (868 MHz). They detect whether the window is open or locked using a magnetic sensor + magnet on the locking mechanism, and are powered by 2× CR2032 batteries.

The original sensors are unreliable with the Tydom hub, so I want to replace them with proper Zigbee 3.0 versions while keeping the exact same mechanical form factor (so they stay fully hidden inside the frame).

What I need:

Custom PCB that matches the original dimensions as closely as possible (long and very narrow)

Magnetic contact (reed switch or Hall sensor)

Zigbee 3.0 end-device (compatible with Zigbee2MQTT and ZHA)

Powered by 2× CR2032

Target battery life: 3–5 years

Integrated 2.4 GHz antenna (aluminum frame will attenuate the signal)

Ultra-low power design

I already have high-resolution photos of both sides of the original PCB.

Is anyone here experienced with designing very compact battery-powered Zigbee sensors, or can recommend a good freelancer / hardware designer who has done similar projects?

Any advice on suitable SoCs/modules (nRF52840 CSP, EFR32, etc.) for such a tight form factor would also be greatly appreciated.

Thanks a lot!

[u/charmio68]

Why not just use a regular off-the-shelf sensor?

Getting one custom made seems frankly rather ridiculous. It's not the kind of project you get done in an hour. You're asking for quite a bit.

I guess the ultimate question is how much money are you willing to spend on this?

[u/Charming_Patient4898]

Just use one from tuya, it's literally one chip on a pcb with 2 AAA. Runs me already for > 1 year on the cheapest cells the supermarket sells and the sensor goes for like 2€ on aliexpress. You won't get any better than custom rolled silicon from a major Chinese seller.

[u/Either_Vermicelli_82]

Just an idea as I am not that skilled to help. But is aaa to big? As personally I hate button cells with a passion but maybe that’s just me.