This application report describes how to implement an ultra-low-powerphoto-diode-based smoke detector using the MSP430F2012 and an externaloperational amplifier that is powered from two AAA batteries. The complete schematicis shown, and the solution is discussed. The complete code is downloadable fromwww.ti.com. In addition, a solution for a piezzo-electric buzzer driver is shown thatproduces >85-dB sound pressure level at a 10-foot distance.