How do I sense activity based off of the current?

There are situations where the mechanical team never confirmed with programming on what they would need to plan for and it is too late to redesign the mechanism and add a proper sensor.

In this case you can sense if there is a game piece by the current on the smart motor controller?

DebouncerFIRST Robotics Competition Documentation

  private SmartMotorControllerConfig smcConfig = new SmartMotorControllerConfig(this)
    .withControlMode(ControlMode.CLOSED_LOOP)
    // Feedback Constants (PID Constants)
    .withClosedLoopController(50, 0, 0, DegreesPerSecond.of(90), DegreesPerSecondPerSecond.of(45))
    .withSimClosedLoopController(50, 0, 0, DegreesPerSecond.of(90), DegreesPerSecondPerSecond.of(45))
    // Feedforward Constants
    .withFeedforward(new ArmFeedforward(0, 0, 0))
    .withSimFeedforward(new ArmFeedforward(0, 0, 0))
    // Telemetry name and verbosity level
    .withTelemetry("ArmMotor", TelemetryVerbosity.HIGH)
    // Gearing from the motor rotor to final shaft.
    // In this example gearbox(3,4) is the same as gearbox("3:1","4:1") which corresponds to the gearbox attached to your motor.
    .withGearing(new MechanismGearing(GearBox.fromReductionStages(3, 4)))
    // Motor properties to prevent over currenting.
    .withMotorInverted(false)
    .withIdleMode(MotorMode.BRAKE)
    .withStatorCurrentLimit(Amps.of(40))
    .withClosedLoopRampRate(Seconds.of(0.25))
    .withOpenLoopRampRate(Seconds.of(0.25));

  // Vendor motor controller object
  private SparkMax spark = new SparkMax(4, MotorType.kBrushless);

  // Create our SmartMotorController from our Spark and config with the NEO.
  private SmartMotorController sparkSmartMotorController = new SparkWrapper(spark, DCMotor.getNEO(1), smcConfig);

  private Debouncer statorDebounce = new Debouncer(0.1); // Debouncer to prevent rapid changes in 0.1s

  /**
   * Game piece is detected if you're using over 40A current for more than 0.1s
   */
  public boolean isGamePieceIn() {
      return statorDebounce.calculate(sparkSmartMotorController.getStatorCurrent().gte(Amps.of(40))); 
  }