Based on cheap standard ESP8266 (and ESP32) boards programmed in Arduino IDE 1+ year operation on 1200mAh or 18650 battery For-ever operation with a small solar panel (80x55mm) ESP-Now receiver ...

Default value for maximum measurement distance is 4m, since HC-SR04 sensor can't measure reliably beyond that. However, if you are using another sensor or if you you don't care about distances larger ...