A red light flashing on either the Pebble or the Base indicates that the device is low on battery and it will not turn on. If the Base is flashing red, plug it into a power source. If the Pebble is flashing red, connect the Pebble to the Base using the USB cable. Make sure the Base is also plugged in otherwise the Pebble will not charge.
Smart Nora can still function while charging, but both the Pebble and the Base need approximately 3 hours to become fully charged.