I second Zigbee.

• There’s plenty of devices available.
• Battery life is amazing.
• zigbee2mqtt is an easy way to bring those messages into your regular IP network; they have a huge list of supported devices.
• Once translated to MQTT, you can hook any automation onto it you want: a python script, home assistant, or my recommendation in this case, NodeRED. NodeRED has a module for zigbee2mqtt that is very well integrated to just know all devices registered on your zigbee network and stringing flows together is actually fun once you get the hang of it. Plus, there is no upper bound to flow complexity.
• Gateway device can be a sonoff zigbee USB coordinator and the whole thing can comfortably run on a rpi3.