Soil Moisture Sensor Module with Buzzer [3V]

The Plant Watering Alarm V2.4 is a compact, capacitive soil moisture sensor designed to remind you when a plant needs water. Instead of resistive sensing, it uses a capacitive probe that does not make electrical contact with the soil, avoiding electrode corrosion and soil electrolysis for better long-term accuracy and battery life. When the soil dries below a user-set threshold, the module emits short chirps through its built-in piezo buzzer. As moisture continues to drop, the chirp rate increases, giving a clear audible warning. A push button lets you set the dry point individually for each plant, and an ambient light sensor keeps the alarm silent at night. The device is built around an ATTINY44A microcontroller, runs on a 3V CR2032 coin cell battery (not included), and measures 140 × 15 mm. It also exposes ISP and I2C headers for programming and expansion, making it suitable for houseplants, greenhouse irrigation alerts, and agricultural research projects. This soil humidity detector is a practical, low-maintenance solution for preventing drought stress in plants.