Each such device uses an antenna to pick up an existing signal and convert it into tens to hundreds of microwatts of electricity.
Initial implementations can communicate over several feet of distance, even if the transmission towers are up to 10.5 kilometres (6.5 mi) away.
Transmission rates were 1k bits per second between devices situated 0.45 metres (1 ft 6 in) apart inside and 0.75 metres (2 ft 6 in) apart outside, sufficient to handle text messages or other small data sets.
[2] Later implementation uses Wi-Fi,[3] Bluetooth,[4] FM radio[5] and LoRa transmissions.
[10] In 2021, researchers integrated RF backscatter with Li-Fi to achieve greater range via PassiveLiFi.