Using the LM3909 integrated circuit can be made a continuity tester using a few simple electronic components. Dimensions that can be achieved this continuity tester is extremely low. Miniature speaker sounds when the resistance of the probe is between 0 and 100 ohms. Differences of 5 ohms are translated into corresponding variations in output volume.
The battery has a relatively long life because the power consumption of continuity tester is only 30 mA when the input terminals are shorted.