Scream at Zero Decibels

I am a single father, and my daughter Xiao Ya has recently kept saying that there is a "monster" talking to her in her room, keeping her from sleeping. To ease her mind, I bought a state-of-the-art remote video monitoring system and installed it in her room. This system is extremely sensitive — as long as there is a little sound or vibration, my phone will pop up an alert. The first night, I sat in the living room watching the feed on my phone. Xiao Ya was sleeping soundly, and the screen showed "0 decibels". I went to bed feeling satisfied. The second night, it was still "0 decibels", everything was peaceful. The third night, on a whim, I wanted to test if the machine was broken. I walked into my daughter's room, and deliberately clapped my hands hard in front of the monitor. I went back to the living room to check my phone, and the screen showed the volume of my clap just now was "90 decibels" — the machine wasn't broken. I breathed a sigh of relief, and just as I was about to close the screen, I accidentally glanced at the three-day "historical volume data chart". The second I saw the data clearly, every hair on my body stood on end. I didn't even dare turn around to look at my daughter's bedroom door behind me, and jumped straight off the second-floor balcony.