If only your plants could let you know when they need a drink—fortunately, these sensors are the next best thing. An innovative moisture sensor triggers the decorative flower, changing color based on need: flashing green means all is well— but when you see red, it’s time to add a splash of water. Indoor use. Plastic; uses 1 AAA battery each (not included). Set of two, 7½" x 1¾" dia.