Wanted my Christmas tree trains to drive automatically (only) when someone is in the living room, so first I made them remote-controlled and then integrated them into Home Assistant. This method is also great for many other battery-powered devices.

RF remote and 3-12v wireless relay: https://a.aliexpress.com/_EyL3BXe
ESP32 DevKit: https://a.aliexpress.com/_EwVZblj
RF transmitter and receiver boards: https://a.aliexpress.com/_EvCDl0d
ESPHome config:
Receiver: https://esphome.io/components/remote_receiver.html
Transmitter: https://esphome.io/components/remote_transmitter