Plant-based sensors like leaf thickness and electrical capacitance were studied to see if they can show when plants are stressed from lack of water. The researchers used a tomato plant in a controlled environment for 11 days, changing the soil moisture levels to see how the plant responded. They found that leaf thickness changed more when the plant was really dry, and electrical capacitance increased when the plant was getting light, showing it was doing photosynthesis. These changes stopped when the plant was very dry, suggesting that these measurements can tell us if a plant needs more water.