The PiGlow costs just $12.99 (from Amazon) (note: just increased to $20.37!!) so this will be one of the cheaper ways to implement ISS-Above.
The video below will give you some idea of how the LED / Color displays tell you how long until the next pass of the ISS.
This is what the LED’s do.
Every few minutes:
If the next pass is over 1 hour they flash RED x the number of hours to the next pass
If the next pass is 1 hour or less they flash GREEN for every 10 minutes. E.g. if it is 40 minutes they will flash green four (4) times
If the next pass is less than 10 minutes they flash BLUE for the number of minutes
Then… when the overflight is happening the LED color display will start flashing ALL DIFFERENT COLORS. Initially – as the ISS is on the horizon and far from you it will flash slowly but as it gets closer and higher in the sky it will start flashing/blinking faster and faster.