Classic MySensors Battery node based on atmega328p and radio nrf24l01 + Si7021/BME/SHT sensor.
On board there is a stub ncp1400, which theoretically two AAA batteries can land up to 0.8v. Consumption in sleep mode with fresh 3.1V batteries turned out to be 5.5 μA, and for discharged up to 2.3 V - 4.5 μA. In the transmission mode on fresh 3.1V - 24mA, on discharged up to 2.3V - 45mA.