A very simple but effective Short Sniffer (Continuity Tester). Original idea & plan courtesy by Douglas Booth for the Nutsand Volts magazine, see below: https://www.nutsvolts.com/magazine/article/build-a-continuity-tester I have made a number of alterations to the original; - replaced the large SMD N-Channel MOSFETS with simple TO-92 ones. - changed the original value of 2MΩ for R16 to 1MoΩ as auto shutoff was well over 3 minutes, now it'll shutoff at around 2 minutes. - added a micro USB port for power. - changed form using AAA batteries to 2 x CR2032 coin cells for space saving. - altered the resistor values on the comparator circuit, now only detects continuity under ~1Ω, basically a short. - added a MOSFET soft switch to automatically switch to USB power if connected & then back to battery when disconnected. - added an LDO for consistant VCC on device despite the varying incoming voltage. - changed the values of some resistors & the capacitor in the oscillator circuit to play better with the new comparator values. Board is designed to fit directly in a Hammond enclosure 1591XXM, specifically I am using the 1591XXMBTU. Uses ~12mA when on but in standby before autoshutoff ~65mA when in use, i.e. buzzer & LED on ~1.9µA in sleep mode (approx 12 years standby from 200mAh CR2032 battery) Thanks for looking.