Logic Probe Project Kit - 

A simple and effective alternative to testing with multimeters or oscilloscopes, the logic probe is a convenient tool that provides feedback with just three LEDs. Fast and intuitive, the output shows the following conditions at a glance: On, Off, Floating and Oscillating. As long as the probe has a common ground with the circuit to be tested, it will show one of these four results. Supplied in kit form, the probe is great for classroom environments where it can be used for practical circuit building while comprehensive documentation will demonstrate how the probe works.