Xiaoyan Contact & Temperature Sensor
The Zigbee-based Smart Home kit is solid and works great with Apple HomeKit, allowing you to create automations with all your other HomeKit supported accessories, depending on whether you’re opening or closing your door or windows. The Contact sensor does require the Xiaoyan Home Center hub, but assuming you’ve already got that in place, this is one of the best performing contact sensors and definitely one of the least expensive.