The SparkFun H2OhNo! is a build-it-yourself water sensor alarm kit based on the ATtiny85 microcontroller. When water bridges the sense pins, the buzzer sounds and the LED starts blinking — perfect for detecting leaks near water heaters, appliances, or in submersible electronics projects.

Beyond its default water alarm function, the H2OhNo! serves as a compact ATtiny85 development board with a buzzer, LED, coin cell battery, and analogue/digital sensor capability. It can be reprogrammed for custom projects using the Arduino IDE.

Key Features

• Water Detection Alarm – Buzzer and LED activate when water is detected
• ATtiny85 Development Board – Reprogrammable for custom projects
• Coin Cell Powered – CR2032 battery for portable, standalone operation
• Analogue & Digital Sensing – Connect additional sensors
• Soldering Kit – Great for learning to solder

Specifications

• MCU: ATtiny85 (pre-programmed)
• Power: CR2032 coin cell battery
• Buzzer: 2 kHz piezo speaker
• Dimensions: 22.86 × 52.07mm (0.90" × 2.05")

Ideal For

• Water leak detection near appliances
• Learning to solder through-hole components
• ATtiny85 programming introduction
• Custom buzzer/sensor projects

Package Contents

• 1× H2OhNo! PCB
• 1× ATtiny85 (pre-programmed)
• 1× 8-Pin DIP Socket
• 1× 20mm Coin Cell Battery Holder
• 1× CR2032 Coin Cell Battery
• 1× Slide Switch
• 1× 2 kHz Piezo Speaker
• 1× Super Bright Red LED
• 1× 0.1 µF Capacitor
• 2× Jumper Wires

Resources

• H2OhNo! Hookup Guide
• Schematic (PDF)
• ATtiny85 Datasheet (PDF)
• GitHub Repository