Here we could write a user guide for xDrip and/or xDrip+.
xDrip+ Settings:
Settings / xDrip+ Display Settings / Smooth Sensor Noise
With noise smoothing on, the low prediction alarm will not sound if the noise level is too high to avoid reacting to trend changes that are just due to noise. The ⚠️ symbol will appear when the noise level is high enough that the value gets smoothed to try to compensate. The trend arrow will vanish when noise is really high that trend calculation doesn't make sense. The idea is to get through small periods of noise with minimal disruption. There is only so much it can do though.