The Weather Predicting Clothes Pegs, by Oliver MacCarthy, know when it’s going to rain.

A latching mechanism allows the Peg to fix itself shut when the system forecasts rainfall, physically preventing you from hanging your clothes out on the line. The movement of the latch is actuated by a micro-solenoid controlled by pulsing electrical commands from the Peg Holder. The Peg Holder incorporates specifically designed micro-controller circuits and software to forecast rainfall.

Each peg knows when it is being used: when you remove it from the holder it stops forecasting the weather and remains in the same free or locked mode until you put it back.