Left: STSP model light curves occulting spots of various radii and the Spitzer photometry of TRAPPIST-1 b. Right: the corresponding discrepancy between the data and the STSP model for each radius. We find that the photometry is insensitive to spots smaller than R_spot/R_⋆ < 0.04, which is similar in size to the smallest sunspots—so small-scale magnetic activity may still be lurking undetected within the transit chords.