You need to work on your basic knowledge of stepper motors first. What you describe in your original post is right for a 4-phase unipolar motor. That would require 5 wires minimum if a common ground is used, 6 wires for a common ground per phase, or 8 wires if the coils are independent. But you later say there are only 4 wires going to the motor, which means you have a TWO-phase bipolar stepper motor. (6 and 8 wire unipolar motors can wired in a bipolar configuration. 5-wire motors can't.)
Most motors you come across in consumer-level 3-d printers are going to be bipolar. The full-step sequence for the a two-phase bipolar motor is accomplished by reversing the phases in sequence like so: ++, +-, --, -+, ++. For half-stepping you it would be: ++, +0, +-, 0-, --, -0, -+, 0+, ++. For microstepping you keep dividing the number of steps between full-range + and -, trading torque for precision. Some degree of microstepping is usually used in printers...you don't need a huge amount of torque. The really good drivers will actively switch between full-stepping and microstepping as required.
Anyway, back to the actual problem. I'd suggest the easiest way to is simply to put a cheap camera pointed at the device with software set up to detect movement. If it fails to detect movement for a configurable amount of time, sound the alarm for someone to check on it.