HomeKit’s ecosystem is fantastic, but the directly compatible devices can get expensive. 25 for a smart plug, $40 for a door sensor – it really adds up quickly. There are plenty of cheaper smart home devices available on Amazon, from $6 smart plugs to $25 cameras, outside the HomeKit ecosystem. Thankfully, many of these otherwise unsupported devices can be brought into HomeKit with the use of Homebridge software.
Link: Use non-HomeKit devices in your HomeKit-enabled smart home with HOOBS