察觉 (chá jué) means 'to sense, perceive, or detect' — it emphasizes becoming aware of something subtle through careful observation or intuition. It is more deliberate and formal than 发现 (fā xiàn 'discover, notice'), and more focused on subtle cues than 发觉 (fā jué 'realize, become aware of'), which often implies a sudden realization. Use 察觉 when the awareness comes from active attention or sensitivity.