This revision had been tweaked for lower power overall. In addition it allows for Panasonic ultra low power PIR sensors to be installed instead of the default chinese HC-SR501 sensors. These Panasonic sensors are much smaller and available in idle consumption as low as 1uA, although they come at a steep price. It also features an optional BME280 temperature/humidity/atm-pressure sensor. The power switch has changed to a much more robust part. There are some solder jumper pad changes and new jumpers that allow more flexibility. The charging rate was changed to a default of 212mA (4.7K resistor). Pullups (4.7K) were added to SCL/SDA pins. An antenna through hole was added so it’s easy to route it straight to the back cover slot. A charge enable solder jumper was added – this is useful when powering from 3XAA/AAA batteries – cut it open to disable charging, resolder to re-enable it.
Revision2 changed to PCB ENIG gold finish and fixes some bugs, most notably the FTDI chip addition of 27ohms inline on the D+/D- traces for better signal integrity. Below are some shots and details of these changes.