This acoustic/audio ohmmeter is a compact (< 5×5 cm PCB) and low power (< 1 mA on open circuit, ~4 mA on short circuit). Silicon parts (U1, D1, D2) are placed in a DIP20 socket for a case when you “measure” a charged high voltage capacitor which will blow the parts up.
Maximum current through the test probes is 1.5 mA.
Sound pitch for low resistances (<100 Ω) is easily distinguishable, great tool! Even for very high resistances (> 100 kΩ) you can still hear a slow clicking.