Bangle.js 2 replacing vibration motor with a buzzer

So you've got HRM_SDA/HRM_SCL/UARX/UATX - that's 4 pins?

I don't know of others I'm afraid, but you could always look at using an I2C or OneWire IO expander? You could glue a chip to the PCB and then wire from that to the pins.

OR if it's just for buttons, connect each button to one IO pin with a resistor to GND, then when you see the IO pin drop to GND in a setWatch, remove the watch, set the pin high and then lower it, and see how long it takes to hit 0 again, and the time taken will depend on the value of the resistor and hence the button.

Something like:

function buttonWatch() {
setWatch(function(a) {
  PIN.set();
  setWatch(function(b) {
    print(b.time - a.time);
    buttonWatch();
  }, PIN, { edge:"falling"});
  PIN.read();
}, PIN, { edge:"falling"});

buttonWatch();

If it works well enough then potentially you could even use 2^n resistor values so you can detect more than one button being held at a time