You put it into the soil near a plant and it emits a tiny chirp when the soil is dry, reminding you to water the plant. Chirp uses capacitive humidity sensing as opposed to resistive humidity sensing, this means, it does not make an electric contact with the soil, avoiding electrode corrosion and soil electrolysis and resulting in better accuracy and longer battery life.

The alarm level can be set for each plant individually. As water is consumed by the plant, Chirp will detect the low moisture level and will start to emit rare short chirps. As more water evaporates, Chirp will increase the alarm rate. Chirp can detect if it's day or night by measuring the amount of ambient light and will not make noise when it's dark.