A0 has two PCBs; one contains the ESP32 processor module, while the other contains the OBD2 connector and interface electronics. The upper PCB has a single momentary pushbutton (requires removing the case to access) and a single green status LED clearly visible through the top of the smoked case. A0 can communicate via WiFi and Bluetooth, or using the built-in microUSB port.
A0 uses the very popular Espressif ESP32, both as the application processor and the WiFi/BT radio processor.
Here is the link to the Espressif ESP32-WROOM32 datasheet: https://www.espressif.com/sites/default/files/documentation/esp32-wroom-32_datasheet_en.pdf