Do I not need the voltage divider? Or is just bad design by Sparkfun?
When using a 5.0Vdc Input, PIO's require a voltage divider. A good choice is 10K ohm series with 20K to Ground. PIO's are 0-3.3Vdc not 5 volt tolerant.
The remote unit can be powered from 3.3V up to 6V for easy battery attachment. All signal pins on the remote unit are 3V-6V tolerant. No level shifting is required. Do not attach this device directly to a serial port. You will need an RS232 to TTL converter circuit if you need to attach this to a computer.