ESP8266 Community Forum

torntrousers wrote:Have you tried it to see what range you get with the ESP without an amplifier? 500m might be possible without an extra amp (if its line-of-sight without things in the way).

Im still waiting for my ESPs

There are commercial CAN BUS wireless systems ($$$) that apparently use part 15 radios at 100 mW at 900 MHz to get > 1 mile.

Some discussion about what might be involved in DIY wireless CAN BUS here.