Dropped $70 on a "smart" plant sensor that told me my fern needed water after it was already dead
Bought one of those wifi moisture probes back in March thinking it would save my plants, and it just kept sending me "all good" alerts while my fern turned brown and crunchy in two weeks. Turns out the probe only read the top inch of soil and the roots were bone dry the whole time, so it kept telling me water was fine. What's the dumbest smart device you regret buying?