```ts
function waveCount(readings: number[]): number {
  if (!readings || readings.length < 2) return 0;

  let count = 0;
  for (let i = 1; i < readings.length; i++) {
    const current = readings[i];
    const previous = readings[i - 1];

    if ((current > 0 && previous <= 0) || (current < 0 && previous >= 0)) {
      count++;
    }
  }

  return count;
}
```