Amazon.com: UbiBot RS485 PT-100 Thermocouple Temperature Probe, Platinum Resistor Sensor for Extreme Heat or Cold, Monitor -200 to 400 C,Audio Plug, for GS1 Device only : Industrial & Scientific
StompBoXed - The Guitar Pedal Builders Repository: Build an Audio Probe - Diagnose Problems
Specialized probes
How to make an audio probe and use it for troubleshooting pedals : r/diypedals
Custom RF & Audio Probe Set for Eico 147/147A & 145A Signal Tracer – Assembled | Inox Wind
Build a Audio and RF Signal Tracer using a Guitar Amplifier - YouTube
How To: Audio Probe | The Peasant Blog
Audio Probe Kit
RF & AUDIO PROBE SET FOR HEATH KIT T3 SIGNAL TRACER | Inox Wind