I recently decided to dip into the Smart Home world in a more serious way. I've had a few IKEA smart power adapters but I was keeping away from the more expensive larger items like security systems, video door bells and smart locks until I was able to do a bit more research on them.
In Europe the selection of official HomeKit approved devices isn't as good as our US cousins have it. Having said that, one smart lock device that piqued my interest was the Nuki Smart Lock 2.0 system.
This device attaches to your door on the inside so the outside is the same as before. There is no expensive locksmith work to be carried out...so long as your door is compatible. Nuki have a great Door Compatibility guide on their site that's really useful. However, as my door had a thumb knob on the inside I wasn't 100% sure if the Nuki Smart Lock would actually work on my door.